- Email: [email protected]
Conceptual model: The aerohemodynamics metatheory
Teaching and Learning in Nursing (2008) 3, 115–120
www.jtln.org
Conceptual model: The aerohemodynamics metatheory Darlene Sredl PhD, RN⁎ University of Missouri at St. Louis, St. Louis, MO 63121, USA KEYWORDS: Aerohemodynamics theory; Conceptual model; Flight nurses
Abstract Nursing in the 21st century demands new conceptual models to guide practice within foreign ambient environments that pose complicated threats to life and well-being. Knowledge development through research must study variables of interest within this foreign ambient environment that sustains the dynamic relationship of the variables within the nursing metaparadigm: health, environment, person, and nursing. This article describes a new conceptual model based on the aerohemodynamics theory. The aerohemodynamics conceptual model applies material from every aspect of the flight environment that is necessary to sustain life: oxygen, temperature, pressure, and positional comfort. The conceptual model of the aerohemodynamics theory provides a framework interrelating the dynamics of physiology with stressors endemic within the flight environment. Once cognizant of the physiological, psychological, environmental, ergonomical, and task-related stressors, a nurse can appropriately care for patients in the airborne environment. In 2002, commercial airlines transported over 2 billion passengers. Although the incidence of death onboard an aircraft is low, occurring only 0.1–3,000,000 passengers per year, the incidence of injury or cardiopulmonary insult is much higher at 1–14,000–40,000 pssengers per year. © 2008 National Organization for Associate Degree Nursing. Published by Elsevier Inc. All rights reserved.
1. Introduction Nursing in the 21st century demands new conceptual models to guide practice within foreign ambient environments that pose subtle yet complicated threats to life and well-being. Knowledge development through research must study variables of interest within this foreign ambient environment that sustain the dynamic relationship of the variables within the nursing metaparadigm: health, environment, person, and nursing.
1.1. Background and definition Although the formal version of the conceptual model, the aerohemodynamics metatheory, was only recently unveiled at the Western Region Canadian Association of Schools of
Nursing Educational Conference (February 2006), this American nursing theory took 25 years to formulate. The original aerohemodynamics theory (Sredl, 1983) evolved from nursing aviator observations that different airborne conditions led to different physiological effects upon a body subjected to those conditions, hence the derivation of the term aero/hemo/dynamics or the dynamic interrelationship of the blood (hemo) with the stressor forces of the air (aero). This short definition evolved quite naturally from the composition of the aerodynamic forces that were found to be acting upon the body at altitude. Defining and structuring the variable relationships that ultimately yielded the empiric model that guides the practice discipline of nursing took a little longer.
1.2. Necessity for a paradigm shift ⁎ Corresponding author. Tel.: +1 314 516 7060 (Office), +1 636 391 9277 (Home). E-mail address: [email protected]
Paradigms, as Kuhn (1970) defined, are laws or principles that most members of a particular scientific discipline hold to
1557-3087/$ – see front matter © 2008 National Organization for Associate Degree Nursing. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.teln.2008.04.003
116
D. Sredl
Fig. 1
Conceptual model: the aerohemodynamics theory.
be true and so guide practice. Nursing paradigms guide thinking about practice applications but also provide a framework for research to gain further insight in expanding the nursing knowledge base. The need for a conceptual model to guide practice in a foreign ambient environment was spawned in part by the enormous numbers of people who utilize air travel. Air travel is used as a transportation choice for recreational destinations, as an adjunct to medical treatment, as an air ambulance, as a delivery method for warfare, and as a mechanism whereby space exploration is becoming a commonplace reality (Kuhn, 1970; Sredl, 1983). Empirical research that guides contemporary nursing practice is research that has been done on earth under relatively stable barometric pressure, temperature, and oxygen availability. None of the aforementioned variables are likely to be “normal” in the airborne flight environment, hence the need for this model to be articulated.
2. The aerohemodynamics conceptual model A conceptual model is a set of interrelated concepts that symbolize a particular phenomenon by describing relationships of central concern to the phenomenon of interest as it relates to the metaparadigm of nursing: person, environment, health, and nursing. Fawcett (1995, 2005) further refines the definition of conceptual model to include concepts and the establishment of relationships between those concepts. Kuhn (1970) outlines some of the characteristics of a model as it pertains to a scientific discipline. Acceptance by a community of scientists, providing a basis for practice, and being
open-ended to serve as a guide for future research are some of Kuhn's recommendations. Conceptual models must, of necessity, be broad and comprehensive in scope, holistic and universal in application, and if not specifically culturally congruent, at least not culturally discordant. The conceptual model must be a cohesive empiric framework in guiding critical thinking on practice applications, open-ended enough to allow future research so as to refine those applications, and flexible so that other subtheories may be generated from the critical thinking research effort (Fig. 1). A theory, in contrast, is a set of statements that tentatively describe, explain, or predict relationships among concepts representative of some phenomenon. These systematic organized perspectives serve as guides for nursing action in administration, education, research, and practice. Theories contain concepts derived from the conceptual model and propositions that describe relationships between two or more of those concepts.
2.1. Broad scope of application Transforming one's perspective from earth-based nursing research to research performed in a foreign ambient environment is just one way the aerohemodynamics metatheory reflects broad scope and universality. The interworkings of the conceptual model are designed to be applied in a flight environment some distance away from the earth. The distance from earth is one of the aspects of the conceptual model that determine how many and which of the concepts will act upon the body at any given altitude. It is broad and comprehensive in scope. It is holistic and universal in applicability. The aerohemodynamics conceptual model
Conceptual model: The aerohemodynamics metatheory applies material from every aspect of the flight environment that is necessary to sustain life: oxygen, temperature, pressure, and positional comfort. These necessities govern life sustenance for everybody. Because the universality of application does not discriminate, it may also be postulated that the aerohemodynamics conceptual model is culturally congruent. Subtheories may develop, however, with further research to identify substantive changes within the health status of people with certain types of diseases (diseases that are associated with ethnic origin). For example, a child with sickle cell anemia may be more at risk for a sickle cell crisis occurring in the commercial flight environment (30,000– 38,000 ft) not because he is Black, but because his ethnic background places him at higher likelihood of having sickle cell disease, which is triggered into sickle cell crisis under hypoxic conditions.
2.2. Applicability to a broad scope of practice Many of the scientific laws that the aerohemodynamics theory is based upon emanate from the physical sciences. These laws have formed the basis for such therapeutic diagnostics as blood gas theory and ultrasound technology. We turn again to these laws as comprising some of the basic building blocks of the aerohemodynamics theory.
3. Concepts
117 square of the airspeed and inversely with the radius of the turn (a = V2 / r). Acceleration is measured in terms of the units of G force (gravity). There are three types of acceleration forces, linear, radial, and angular, that give rise to three types of G forces: positive, negative, and transverse. Variables that influence the effect of G forces are intensity of the force, duration of the force, rate of the applied force, and site and area over which force is applied to the body.
3.2. Barotrauma Barotrauma is another variable of interest within the aerohemodynamics conceptual model. Dysbarism is a collective term used to describe all of the physiological effects occurring within the body as a direct result of changes in barometric pressure. Barotrauma is tissue trauma resulting from changes in barometric pressure that may be of the following types: sudden decompression syndrome, barotitis media/barosinusitis, or barodontalgia.
3.3. Thermostability A thermostabile environment is one in which the temperature remains constant. The airborne environment produces cold stress because of decreased air temperature, lack of humidity, and reflection of radiant surfaces.
3.1. Acceleration forces
3.4. Gaseous toxicities, diffusion, and vacuolization
Acceleration forces are one variable of interest within the aerohemodynamics conceptual model. All aircrafts maneuver through the air by means of velocity changes and directional alterations. Velocity is the rate of change of position.
Many gaseous abnormalities can affect the individual at altitude. Hypoxia or oxygen deficiency in tissues can affect the individual via many routes. The following are types of hypoxia:
Acceleration is the rate of change of velocity and/or change in rate/direction of that velocity. Deceleration is any reduction in rate and/or direction of velocity. It is sometimes referred to as negative acceleration.
Simple hypoxia is the inability of the body to take in enough oxygen to meet the cellular demands of tissues. Stagnant or circulatory hypoxia is caused by gross malfunction of the circulatory system (e.g., cardiac arrest or G-force venous pooling). Histotoxic hypoxia occurs when tissues are unable to accept and/ or metabolize oxygen due to synaptic bridge barriers such as in disease-causing microbials that render red blood cells (RBCs) ineffective. Hemolyzed hypoxia is a mechanical rupture of RBCs, rendering hemoglobin useless for transport. Hypemic or anemic hypoxia occurs when there is decreased hemoglobin–oxygen affinity (e.g., carbon monoxide [CO] and sickle cell disease). Hypoxia caused by decreased lung capacity occurs when there is minimization of available lung tissue (e.g., atelectasis and penetrating chest wounds).
Acceleration forces occur through one of three defined axes of rotation of an aircraft: roll, pitch, and yaw. An “axis” is a line passing through a body and about which the body revolves. “Roll” is a longitudinal axis of rotation. An aircraft roll axis is an imaginary line drawn from the aircraft's nose through its center of gravity and out to its tail. The aircraft could literally “roll” wing over wing. “Pitch” is a “lateral axis” produced by an imaginary line drawn from wingtip through the center of gravity to wingtip. Climbing and diving (pitching forward or up) are the accelerative motions produced by the lateral axis of pitch. “Yaw” is the “vertical axis” of rotation that occurs when an imaginary line is drawn from the top, through the center of gravity, to the bottom of the aircraft. The aircraft rotates in a horizontal plane around the imaginary axis. Acceleration varies directly with the
Vacuolization is the process of gaseous bubble formation and/or expansion in response to a decrease in atmospheric (barometric) pressure. Rapid pressure decrease causes
118 bubble formation. The following laws of gaseous diffusion apply to situations in the airborne environment: Dalton's law: Total pressure exerted by a mixture of gases is the sum of pressures that would be exerted by each of the gases (partial pressure of each gas), if it alone were present, occupying the total volume. Boyle's law: Volume of a gas will vary inversely as the absolute pressure, whereas the density varies directly as the pressure. Charles' law: All gases, by equal degrees of heat and under the same conditions, expand proportionately just alike. Avogadro's law: For a given mass, pressure, and temperature, the volume of a gas is inversely proportional to its molecular weight. Graham's law of diffusion: Rate at which a gas diffuses is proportional to the square root of its molecular weight (Sredl, 1983).
Carbon monoxide is one of the end products of tobacco consumption. At altitude, the decrease in oxygen tension, coupled with the hemoglobin saturation properties of smoked CO, potentiates the effects of hypoxia. A concentration of 0.01% CO (safe at ground level) reduces the oxygenation of the blood by 10.5% at 10,000 ft. Ozone poisoning is particular to the flight environment. Even small amounts can predispose toward the following symptoms: chest tightening, choking, and anxiety, all of which can mimic a myocardial infarction.
D. Sredl mental, ergonomical, and task-related stressors, a nurse can appropriately care for patients in the airborne environment.
4. Nursing implications In 2002, commercial airlines transported over 2 billion passengers. Although the incidence of death onboard an aircraft is low, occurring only 0.1–3,000,000 passengers per year, the incidence of injury or cardiopulmonary insult is much higher at 1–14,000–40,000 passengers per year. As a passenger, much can be gained from the adoption of the conceptual model of aerohemodynamics theory. A nurse flying as a passenger can utilize the conceptual background to make healthy choices for himself or herself and for his or her families. As an in-flight nurse, air ambulances are now supported both by private aviation companies and by hospitals. The new subspecialty of flight nursing holds appeal for nurses wishing to exercise more autonomy in practice. The Commission on Accreditation of Medical Transport Systems (CAMTS) is the regulating body for medical-flight-related services. The new occupation or professional position of aviation medical/nursing director is now available. The obligation to have a person trained in the aviation physiological sciences is one of CAMTS' requirements for accreditation.
4.1. Acceleration force changes
Radiation is the process whereby electromagnetic waves are emitted from a specific broadcast source (Sredl, 1983). Radiation exposure occurs from a variety of sources at altitude. Radiant energy forms include visible light, radio waves, ultraviolet light, infrared light, x-rays, gamma rays, and cosmic rays (Sredl, 1983). Because most commercial aircrafts fly at altitudes above the clouds, there is no filter for the sun's ultraviolet rays. Also, the aircraft is in continuous communication with a radio-signal relay station via the continuously operating transponder. This transponder signal emits radiation signals, as does communication from the aircraft to control tower. Ultrasound devices emit low levels of radiation. Radio frequency (10 KHz–300 GHz) radiation insult is strongly communication frequency dependent (Sredl, 1983). Although the most significant circumstances of radiation exposure occur on space flights, especially those of long duration, radiation exposure from the aforementioned sources can be cumulative and especially deleterious to pregnant crew members or passengers (Control, 2003).
Some of the physiological effects of acceleration forces upon the body include venous engorgement in upper or lower extremities that can lead to thrombus formation or loss of consciousness (Sredl, 1983; Wilson, Reis, & Tripp, 2005). Electroencephalogram changes and eye activity changes also occur under acceleration stress, with blink inhibition and the possibility of cognitive changes occurring in later stages of pressure (Wilson et al., 2005). Studies demonstrate that cardiac responses to linear acceleration result in transient increases in heart rate and blood pressure (Jauregui-Renaud, Reynolds, Bronstein, & Gresty, 2006; Radtke, Popov, Bronstein, & Gresty, 2000; Yates, Aoki, Bronstein, & Gresty, 1999). Acceleration forces significantly hasten motion sickness symptoms because they intermittently alter rotation directions, thus altering vestibular input (Bonato, Bubka, & Story, 2005). In addition, pilots in high-performance aircraft including pilots in fighter and experimental aircraft have experienced significant physiological threats to acceleration-induced cerebral perfusion insults because of acceleration in the head-to-foot or z axis (McKinley, Tripp, Bolia, & Roark, 2005).
3.6. Formal definition
4.2. Motion sickness susceptibility
The conceptual model of the aerohemodynamics theory provides a framework interrelating the dynamics of physiology with stressors endemic within the flight environment. Once cognizant of the physiological, psychological, environ-
Survey studies of gender susceptibility to motion sickness have shown a wide variation of results. Surveys of motion sickness at sea demonstrate a 5-to-3 female-to-male risk ratio for vomiting (Lawther & Griffin, 1988). One theory relating
3.5. Radiation exposure
Conceptual model: The aerohemodynamics metatheory this consequence to female hormone or menstrual cycle remains contradictory (Cheung, Heskin, Hofer, & Gagnon, 2001). A study by Golding, Kadzere, and Gresty (2005), however, concluded that there was a greater trend for female susceptibility to motion sickness at Menstrual Day 5 (Golding et al., 2005).
4.3. Barotrauma The ambient pressure changes that can initiate the tissue trauma known as barotraumas exhibit markedly in the ear (Klokker, Vesterhauge, & Jansen, 2005). Ear barotrauma is characterized by pain and sensation of pressure, diminished hearing, and, sometimes, dizziness (Klokker et al., 2005). Not usually a problem on ascent, the need to equalize pressure in the inner ear compartment on descent may cause rupture of the eardrum if techniques like the Valsalva maneuver or swallowing do not result in the desired pressure equalization (Klokker et al., 2005). It can readily be seen how this attempt at pressure equalization can be more problematic for infants, young children, individuals of all ages who are mentally or cognitively impaired, and comatose patients on descent from altitude (Klokker et al., 2005).
4.4. Thermostability Heat stress and cold stress situations can, and do, occur at altitude. The body's thermoregulatory controller issues different metabolic rates for different areas of the body. These weighted thermal thresholds respond to indicators in different segments of the body according to tissue composites of core, muscle, fat, and skin (Xiaojiang, Berglund, Cheuvroni, Endrusick, & Kolka 2004). Different areas of the body have different heating and cooling requirements and need support systems in the foreign airborne environment to provide life-sustaining comfort levels (Xiaojiang et al., 2004). A pilot study of exposure to cold (N = 10) by Makinen et al. (2005) found that cold exposure affects postural control due to suppression of tendon-reflex responses. This result indicates a greater need for vigilance in flight as older people or people of any age exposed to cold stress are more likely to be at risk for falls.
4.5. Gaseous toxicities The lack of oxygen that may be experienced at altitude can pose ominous risks for passengers. It has been demonstrated that cerebral metabolism decreases with increased cerebral hypoxia (McKinley et al., 2005). Reductions in mental functioning have been shown to occur when oxygen pressure is reduced by only a small amount (Bolgg & Gennser, 2006). Normally, the body's circulating leukocyte count rises as a response to a variety of stressful situations, but in vitro studies conducted in extreme localized hypoxic situations have shown that neutrophil phagocytic function is suppressed (Lingaas & Midtvedt, 1987; Thake, Mian, Garnham, & Mian, 2004).
119 The emergence of gaseous bubbles (vacuolization) in the bloodstream such as occurs during transition through different pressure gradients can now be detected using Doppler ultrasound technology (Payne & Chapell, 2005; Sredl, 1983).
4.6. Radiation and other safety hazards Hazards of working in a radiation-enhanced environment have not been as adequately studied in a commercial aircraft as in the cumulative effects of space radiation on crew members of extended-duration flights. These studies, however, have resulted in a new medication (Amifostine) designed to prevent some of the symptoms of ionizingradiation-induced damage (Epelman & Hamilton, 2006).
5. Nursing research Nursing research opportunities at all levels exist in the flight environment. Many subtheories posited around the modeling/role modeling theory are evolving. The modeling/ role modeling theory focuses on supportive systems in the environment. All of the life-sustaining efforts employed in the flight environment fit these criteria. The airborne environment is composed of nonlinear complex relationships (Beard, 1995). These relationships provide the framework for the empiric collections of facts, assumptions, hypotheses, and nursing critical thinking that comprise the aerohemodynamics conceptual model.
References Beard, M. E. (Ed.). (1995). Theory Construction and Testing. Lisle: Tucker Publications. Bolgg, S., & Gennser, M. (2006). Cerebral blood flow velocity and psychomotor performance during acute hypoxia. Aviation, Space and Environmental Medicine, 77(2), 107−113. Bonato, F., Bubka, A., & Story, M. (2005). Rotation direction change hastens motion sickness onset in an optokinetic drum. Aviation, Space, and Environmental Medicine, 76(9), 823−827. Cheung, B., Heskin, R., Hofer, K., & Gagnon, M. (2001). The menstrual cycle and susceptibility to Coriolis-induced sickness. Journal of Vestibular Responses, 11, 129−136. Control, C. F. D. (2003). Acute radiation syndrome, fact sheet for physicians. Atlanta: CDC. Epelman, S., & Hamilton, D. (2006). Medical mitigation strategies for acute radiation exposure during spaceflight. Aviation, Space and Environmental Medicine, 77(2), 130−137. Fawcett, J. (1995). Analysis and evaluation of conceptual models of nursing. Philadelphia: F.A. Davis Company. Fawcett, J. (2005). Contemporary nursing knowledge: Analysis and evaluation of nursing models and theories (2nd ed.). Philadelphia: F.A. Davis Company. Golding, J., Kadzere, P., & Gresty, M. (2005). Motion sickness susceptibility fluctuates through the menstrual cycle. Aviation, space, and Environmental medicine, 76(10), 970−973. Jauregui-Renaud, K., Reynolds, R., Bronstein, A., & Gresty, M. (2006). Cardio-respiratory responses evoked by transient linear acceleration. Aviation, Space, and Environmental Medicine, 77(2), 114−120.
120 Klokker, M., Vesterhauge, S., & Jansen, E. (2005). Pressure-equalizing earplugs do not prevent barotrauma on descent from 8000 ft cabin altitude. Aviation, Space, and Environmental Medicine, 76(11), 1079−1082. Kuhn, T. (1970). The structure of scientific revolutions (2nd ed.). Chicago: University of Chicago Press. Lawther, A., & Griffin, M. (1988). A survey of the occurrence of motion sickness amongst passengers at sea. Aviation, Space, and Environmental Medicine, 59, 399−406. Lingaas, E., & Midtvedt, T. (1987). The influence of high and low pressure on phagocytosis of Escherichia coli by human neutrophils in vitro. Aviation, Space and Environmental Medicine, 58, 1211−1214. Makinen, T., Rintamaki, H., Korpelainen, J., Kampman, V., Paakonen, T., Oksa, J., Palinkas, L., Leppaluoto, J., & Hassi, J. (2005). Postural sway during single and repeated cold exposures. Aviation, Space and Environmental Medicine, 76(10), 947−953. McKinley, R., Tripp, L., Jr, Bolia, S., & Roark, M. (2005). Computer modeling of acceleration effects on cerebral oxygen saturation. Aviation, Space, and Environmental Medicine, 76(8), 733−737.
D. Sredl Payne, S., & Chapell, M. (2005). Automated determination of bubble grades from Doppler ultrasound recordings. Aviation, Space and Environmental Medicine, 76(8), 771−777. Radtke, A., Popov, K., Bronstein, A., & Gresty, M. (2000). Evidence for a vestibulo-cardiac reflex in man. Lancet, 356, 736−737. Sredl, D. (1983). Airborne patient care management: A multidisciplinary approach. St. Louis: Medical Research Associates Publications. Thake, C., Mian, T., Garnham, A., & Mian, R. (2004). Leukocyte counts and neutrophil activity during 4 h of hypocapnic hypoxia equivalent to 4000m. Aviation, Space and Environmental Medicine, 75(9), 811−817. Wilson, G., Reis, G., & Tripp, L. (2005). EEG correlates of G-induced loss of consciousness. Aviation, Space and Environmental Medicine, 76(1), 19−27. Xiaojiang, X., Berglund, L., Cheuvroni, S., Endrusick, T., & Kolka, M. (2004). Model of human thermoregulation for intermittent regional cooling. Aviation, Space and Environmental Medicine, 75(12), 1065−1069. Yates, B., Aoki, M., Bronstein, A., & Gresty, M. (1999). Cardiovascular response to linear acceleration in humans. Experimental Brain Research, 125, 476−484.
www.jtln.org
Conceptual model: The aerohemodynamics metatheory Darlene Sredl PhD, RN⁎ University of Missouri at St. Louis, St. Louis, MO 63121, USA KEYWORDS: Aerohemodynamics theory; Conceptual model; Flight nurses
Abstract Nursing in the 21st century demands new conceptual models to guide practice within foreign ambient environments that pose complicated threats to life and well-being. Knowledge development through research must study variables of interest within this foreign ambient environment that sustains the dynamic relationship of the variables within the nursing metaparadigm: health, environment, person, and nursing. This article describes a new conceptual model based on the aerohemodynamics theory. The aerohemodynamics conceptual model applies material from every aspect of the flight environment that is necessary to sustain life: oxygen, temperature, pressure, and positional comfort. The conceptual model of the aerohemodynamics theory provides a framework interrelating the dynamics of physiology with stressors endemic within the flight environment. Once cognizant of the physiological, psychological, environmental, ergonomical, and task-related stressors, a nurse can appropriately care for patients in the airborne environment. In 2002, commercial airlines transported over 2 billion passengers. Although the incidence of death onboard an aircraft is low, occurring only 0.1–3,000,000 passengers per year, the incidence of injury or cardiopulmonary insult is much higher at 1–14,000–40,000 pssengers per year. © 2008 National Organization for Associate Degree Nursing. Published by Elsevier Inc. All rights reserved.
1. Introduction Nursing in the 21st century demands new conceptual models to guide practice within foreign ambient environments that pose subtle yet complicated threats to life and well-being. Knowledge development through research must study variables of interest within this foreign ambient environment that sustain the dynamic relationship of the variables within the nursing metaparadigm: health, environment, person, and nursing.
1.1. Background and definition Although the formal version of the conceptual model, the aerohemodynamics metatheory, was only recently unveiled at the Western Region Canadian Association of Schools of
Nursing Educational Conference (February 2006), this American nursing theory took 25 years to formulate. The original aerohemodynamics theory (Sredl, 1983) evolved from nursing aviator observations that different airborne conditions led to different physiological effects upon a body subjected to those conditions, hence the derivation of the term aero/hemo/dynamics or the dynamic interrelationship of the blood (hemo) with the stressor forces of the air (aero). This short definition evolved quite naturally from the composition of the aerodynamic forces that were found to be acting upon the body at altitude. Defining and structuring the variable relationships that ultimately yielded the empiric model that guides the practice discipline of nursing took a little longer.
1.2. Necessity for a paradigm shift ⁎ Corresponding author. Tel.: +1 314 516 7060 (Office), +1 636 391 9277 (Home). E-mail address: [email protected]
Paradigms, as Kuhn (1970) defined, are laws or principles that most members of a particular scientific discipline hold to
1557-3087/$ – see front matter © 2008 National Organization for Associate Degree Nursing. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.teln.2008.04.003
116
D. Sredl
Fig. 1
Conceptual model: the aerohemodynamics theory.
be true and so guide practice. Nursing paradigms guide thinking about practice applications but also provide a framework for research to gain further insight in expanding the nursing knowledge base. The need for a conceptual model to guide practice in a foreign ambient environment was spawned in part by the enormous numbers of people who utilize air travel. Air travel is used as a transportation choice for recreational destinations, as an adjunct to medical treatment, as an air ambulance, as a delivery method for warfare, and as a mechanism whereby space exploration is becoming a commonplace reality (Kuhn, 1970; Sredl, 1983). Empirical research that guides contemporary nursing practice is research that has been done on earth under relatively stable barometric pressure, temperature, and oxygen availability. None of the aforementioned variables are likely to be “normal” in the airborne flight environment, hence the need for this model to be articulated.
2. The aerohemodynamics conceptual model A conceptual model is a set of interrelated concepts that symbolize a particular phenomenon by describing relationships of central concern to the phenomenon of interest as it relates to the metaparadigm of nursing: person, environment, health, and nursing. Fawcett (1995, 2005) further refines the definition of conceptual model to include concepts and the establishment of relationships between those concepts. Kuhn (1970) outlines some of the characteristics of a model as it pertains to a scientific discipline. Acceptance by a community of scientists, providing a basis for practice, and being
open-ended to serve as a guide for future research are some of Kuhn's recommendations. Conceptual models must, of necessity, be broad and comprehensive in scope, holistic and universal in application, and if not specifically culturally congruent, at least not culturally discordant. The conceptual model must be a cohesive empiric framework in guiding critical thinking on practice applications, open-ended enough to allow future research so as to refine those applications, and flexible so that other subtheories may be generated from the critical thinking research effort (Fig. 1). A theory, in contrast, is a set of statements that tentatively describe, explain, or predict relationships among concepts representative of some phenomenon. These systematic organized perspectives serve as guides for nursing action in administration, education, research, and practice. Theories contain concepts derived from the conceptual model and propositions that describe relationships between two or more of those concepts.
2.1. Broad scope of application Transforming one's perspective from earth-based nursing research to research performed in a foreign ambient environment is just one way the aerohemodynamics metatheory reflects broad scope and universality. The interworkings of the conceptual model are designed to be applied in a flight environment some distance away from the earth. The distance from earth is one of the aspects of the conceptual model that determine how many and which of the concepts will act upon the body at any given altitude. It is broad and comprehensive in scope. It is holistic and universal in applicability. The aerohemodynamics conceptual model
Conceptual model: The aerohemodynamics metatheory applies material from every aspect of the flight environment that is necessary to sustain life: oxygen, temperature, pressure, and positional comfort. These necessities govern life sustenance for everybody. Because the universality of application does not discriminate, it may also be postulated that the aerohemodynamics conceptual model is culturally congruent. Subtheories may develop, however, with further research to identify substantive changes within the health status of people with certain types of diseases (diseases that are associated with ethnic origin). For example, a child with sickle cell anemia may be more at risk for a sickle cell crisis occurring in the commercial flight environment (30,000– 38,000 ft) not because he is Black, but because his ethnic background places him at higher likelihood of having sickle cell disease, which is triggered into sickle cell crisis under hypoxic conditions.
2.2. Applicability to a broad scope of practice Many of the scientific laws that the aerohemodynamics theory is based upon emanate from the physical sciences. These laws have formed the basis for such therapeutic diagnostics as blood gas theory and ultrasound technology. We turn again to these laws as comprising some of the basic building blocks of the aerohemodynamics theory.
3. Concepts
117 square of the airspeed and inversely with the radius of the turn (a = V2 / r). Acceleration is measured in terms of the units of G force (gravity). There are three types of acceleration forces, linear, radial, and angular, that give rise to three types of G forces: positive, negative, and transverse. Variables that influence the effect of G forces are intensity of the force, duration of the force, rate of the applied force, and site and area over which force is applied to the body.
3.2. Barotrauma Barotrauma is another variable of interest within the aerohemodynamics conceptual model. Dysbarism is a collective term used to describe all of the physiological effects occurring within the body as a direct result of changes in barometric pressure. Barotrauma is tissue trauma resulting from changes in barometric pressure that may be of the following types: sudden decompression syndrome, barotitis media/barosinusitis, or barodontalgia.
3.3. Thermostability A thermostabile environment is one in which the temperature remains constant. The airborne environment produces cold stress because of decreased air temperature, lack of humidity, and reflection of radiant surfaces.
3.1. Acceleration forces
3.4. Gaseous toxicities, diffusion, and vacuolization
Acceleration forces are one variable of interest within the aerohemodynamics conceptual model. All aircrafts maneuver through the air by means of velocity changes and directional alterations. Velocity is the rate of change of position.
Many gaseous abnormalities can affect the individual at altitude. Hypoxia or oxygen deficiency in tissues can affect the individual via many routes. The following are types of hypoxia:
Acceleration is the rate of change of velocity and/or change in rate/direction of that velocity. Deceleration is any reduction in rate and/or direction of velocity. It is sometimes referred to as negative acceleration.
Simple hypoxia is the inability of the body to take in enough oxygen to meet the cellular demands of tissues. Stagnant or circulatory hypoxia is caused by gross malfunction of the circulatory system (e.g., cardiac arrest or G-force venous pooling). Histotoxic hypoxia occurs when tissues are unable to accept and/ or metabolize oxygen due to synaptic bridge barriers such as in disease-causing microbials that render red blood cells (RBCs) ineffective. Hemolyzed hypoxia is a mechanical rupture of RBCs, rendering hemoglobin useless for transport. Hypemic or anemic hypoxia occurs when there is decreased hemoglobin–oxygen affinity (e.g., carbon monoxide [CO] and sickle cell disease). Hypoxia caused by decreased lung capacity occurs when there is minimization of available lung tissue (e.g., atelectasis and penetrating chest wounds).
Acceleration forces occur through one of three defined axes of rotation of an aircraft: roll, pitch, and yaw. An “axis” is a line passing through a body and about which the body revolves. “Roll” is a longitudinal axis of rotation. An aircraft roll axis is an imaginary line drawn from the aircraft's nose through its center of gravity and out to its tail. The aircraft could literally “roll” wing over wing. “Pitch” is a “lateral axis” produced by an imaginary line drawn from wingtip through the center of gravity to wingtip. Climbing and diving (pitching forward or up) are the accelerative motions produced by the lateral axis of pitch. “Yaw” is the “vertical axis” of rotation that occurs when an imaginary line is drawn from the top, through the center of gravity, to the bottom of the aircraft. The aircraft rotates in a horizontal plane around the imaginary axis. Acceleration varies directly with the
Vacuolization is the process of gaseous bubble formation and/or expansion in response to a decrease in atmospheric (barometric) pressure. Rapid pressure decrease causes
118 bubble formation. The following laws of gaseous diffusion apply to situations in the airborne environment: Dalton's law: Total pressure exerted by a mixture of gases is the sum of pressures that would be exerted by each of the gases (partial pressure of each gas), if it alone were present, occupying the total volume. Boyle's law: Volume of a gas will vary inversely as the absolute pressure, whereas the density varies directly as the pressure. Charles' law: All gases, by equal degrees of heat and under the same conditions, expand proportionately just alike. Avogadro's law: For a given mass, pressure, and temperature, the volume of a gas is inversely proportional to its molecular weight. Graham's law of diffusion: Rate at which a gas diffuses is proportional to the square root of its molecular weight (Sredl, 1983).
Carbon monoxide is one of the end products of tobacco consumption. At altitude, the decrease in oxygen tension, coupled with the hemoglobin saturation properties of smoked CO, potentiates the effects of hypoxia. A concentration of 0.01% CO (safe at ground level) reduces the oxygenation of the blood by 10.5% at 10,000 ft. Ozone poisoning is particular to the flight environment. Even small amounts can predispose toward the following symptoms: chest tightening, choking, and anxiety, all of which can mimic a myocardial infarction.
D. Sredl mental, ergonomical, and task-related stressors, a nurse can appropriately care for patients in the airborne environment.
4. Nursing implications In 2002, commercial airlines transported over 2 billion passengers. Although the incidence of death onboard an aircraft is low, occurring only 0.1–3,000,000 passengers per year, the incidence of injury or cardiopulmonary insult is much higher at 1–14,000–40,000 passengers per year. As a passenger, much can be gained from the adoption of the conceptual model of aerohemodynamics theory. A nurse flying as a passenger can utilize the conceptual background to make healthy choices for himself or herself and for his or her families. As an in-flight nurse, air ambulances are now supported both by private aviation companies and by hospitals. The new subspecialty of flight nursing holds appeal for nurses wishing to exercise more autonomy in practice. The Commission on Accreditation of Medical Transport Systems (CAMTS) is the regulating body for medical-flight-related services. The new occupation or professional position of aviation medical/nursing director is now available. The obligation to have a person trained in the aviation physiological sciences is one of CAMTS' requirements for accreditation.
4.1. Acceleration force changes
Radiation is the process whereby electromagnetic waves are emitted from a specific broadcast source (Sredl, 1983). Radiation exposure occurs from a variety of sources at altitude. Radiant energy forms include visible light, radio waves, ultraviolet light, infrared light, x-rays, gamma rays, and cosmic rays (Sredl, 1983). Because most commercial aircrafts fly at altitudes above the clouds, there is no filter for the sun's ultraviolet rays. Also, the aircraft is in continuous communication with a radio-signal relay station via the continuously operating transponder. This transponder signal emits radiation signals, as does communication from the aircraft to control tower. Ultrasound devices emit low levels of radiation. Radio frequency (10 KHz–300 GHz) radiation insult is strongly communication frequency dependent (Sredl, 1983). Although the most significant circumstances of radiation exposure occur on space flights, especially those of long duration, radiation exposure from the aforementioned sources can be cumulative and especially deleterious to pregnant crew members or passengers (Control, 2003).
Some of the physiological effects of acceleration forces upon the body include venous engorgement in upper or lower extremities that can lead to thrombus formation or loss of consciousness (Sredl, 1983; Wilson, Reis, & Tripp, 2005). Electroencephalogram changes and eye activity changes also occur under acceleration stress, with blink inhibition and the possibility of cognitive changes occurring in later stages of pressure (Wilson et al., 2005). Studies demonstrate that cardiac responses to linear acceleration result in transient increases in heart rate and blood pressure (Jauregui-Renaud, Reynolds, Bronstein, & Gresty, 2006; Radtke, Popov, Bronstein, & Gresty, 2000; Yates, Aoki, Bronstein, & Gresty, 1999). Acceleration forces significantly hasten motion sickness symptoms because they intermittently alter rotation directions, thus altering vestibular input (Bonato, Bubka, & Story, 2005). In addition, pilots in high-performance aircraft including pilots in fighter and experimental aircraft have experienced significant physiological threats to acceleration-induced cerebral perfusion insults because of acceleration in the head-to-foot or z axis (McKinley, Tripp, Bolia, & Roark, 2005).
3.6. Formal definition
4.2. Motion sickness susceptibility
The conceptual model of the aerohemodynamics theory provides a framework interrelating the dynamics of physiology with stressors endemic within the flight environment. Once cognizant of the physiological, psychological, environ-
Survey studies of gender susceptibility to motion sickness have shown a wide variation of results. Surveys of motion sickness at sea demonstrate a 5-to-3 female-to-male risk ratio for vomiting (Lawther & Griffin, 1988). One theory relating
3.5. Radiation exposure
Conceptual model: The aerohemodynamics metatheory this consequence to female hormone or menstrual cycle remains contradictory (Cheung, Heskin, Hofer, & Gagnon, 2001). A study by Golding, Kadzere, and Gresty (2005), however, concluded that there was a greater trend for female susceptibility to motion sickness at Menstrual Day 5 (Golding et al., 2005).
4.3. Barotrauma The ambient pressure changes that can initiate the tissue trauma known as barotraumas exhibit markedly in the ear (Klokker, Vesterhauge, & Jansen, 2005). Ear barotrauma is characterized by pain and sensation of pressure, diminished hearing, and, sometimes, dizziness (Klokker et al., 2005). Not usually a problem on ascent, the need to equalize pressure in the inner ear compartment on descent may cause rupture of the eardrum if techniques like the Valsalva maneuver or swallowing do not result in the desired pressure equalization (Klokker et al., 2005). It can readily be seen how this attempt at pressure equalization can be more problematic for infants, young children, individuals of all ages who are mentally or cognitively impaired, and comatose patients on descent from altitude (Klokker et al., 2005).
4.4. Thermostability Heat stress and cold stress situations can, and do, occur at altitude. The body's thermoregulatory controller issues different metabolic rates for different areas of the body. These weighted thermal thresholds respond to indicators in different segments of the body according to tissue composites of core, muscle, fat, and skin (Xiaojiang, Berglund, Cheuvroni, Endrusick, & Kolka 2004). Different areas of the body have different heating and cooling requirements and need support systems in the foreign airborne environment to provide life-sustaining comfort levels (Xiaojiang et al., 2004). A pilot study of exposure to cold (N = 10) by Makinen et al. (2005) found that cold exposure affects postural control due to suppression of tendon-reflex responses. This result indicates a greater need for vigilance in flight as older people or people of any age exposed to cold stress are more likely to be at risk for falls.
4.5. Gaseous toxicities The lack of oxygen that may be experienced at altitude can pose ominous risks for passengers. It has been demonstrated that cerebral metabolism decreases with increased cerebral hypoxia (McKinley et al., 2005). Reductions in mental functioning have been shown to occur when oxygen pressure is reduced by only a small amount (Bolgg & Gennser, 2006). Normally, the body's circulating leukocyte count rises as a response to a variety of stressful situations, but in vitro studies conducted in extreme localized hypoxic situations have shown that neutrophil phagocytic function is suppressed (Lingaas & Midtvedt, 1987; Thake, Mian, Garnham, & Mian, 2004).
119 The emergence of gaseous bubbles (vacuolization) in the bloodstream such as occurs during transition through different pressure gradients can now be detected using Doppler ultrasound technology (Payne & Chapell, 2005; Sredl, 1983).
4.6. Radiation and other safety hazards Hazards of working in a radiation-enhanced environment have not been as adequately studied in a commercial aircraft as in the cumulative effects of space radiation on crew members of extended-duration flights. These studies, however, have resulted in a new medication (Amifostine) designed to prevent some of the symptoms of ionizingradiation-induced damage (Epelman & Hamilton, 2006).
5. Nursing research Nursing research opportunities at all levels exist in the flight environment. Many subtheories posited around the modeling/role modeling theory are evolving. The modeling/ role modeling theory focuses on supportive systems in the environment. All of the life-sustaining efforts employed in the flight environment fit these criteria. The airborne environment is composed of nonlinear complex relationships (Beard, 1995). These relationships provide the framework for the empiric collections of facts, assumptions, hypotheses, and nursing critical thinking that comprise the aerohemodynamics conceptual model.
References Beard, M. E. (Ed.). (1995). Theory Construction and Testing. Lisle: Tucker Publications. Bolgg, S., & Gennser, M. (2006). Cerebral blood flow velocity and psychomotor performance during acute hypoxia. Aviation, Space and Environmental Medicine, 77(2), 107−113. Bonato, F., Bubka, A., & Story, M. (2005). Rotation direction change hastens motion sickness onset in an optokinetic drum. Aviation, Space, and Environmental Medicine, 76(9), 823−827. Cheung, B., Heskin, R., Hofer, K., & Gagnon, M. (2001). The menstrual cycle and susceptibility to Coriolis-induced sickness. Journal of Vestibular Responses, 11, 129−136. Control, C. F. D. (2003). Acute radiation syndrome, fact sheet for physicians. Atlanta: CDC. Epelman, S., & Hamilton, D. (2006). Medical mitigation strategies for acute radiation exposure during spaceflight. Aviation, Space and Environmental Medicine, 77(2), 130−137. Fawcett, J. (1995). Analysis and evaluation of conceptual models of nursing. Philadelphia: F.A. Davis Company. Fawcett, J. (2005). Contemporary nursing knowledge: Analysis and evaluation of nursing models and theories (2nd ed.). Philadelphia: F.A. Davis Company. Golding, J., Kadzere, P., & Gresty, M. (2005). Motion sickness susceptibility fluctuates through the menstrual cycle. Aviation, space, and Environmental medicine, 76(10), 970−973. Jauregui-Renaud, K., Reynolds, R., Bronstein, A., & Gresty, M. (2006). Cardio-respiratory responses evoked by transient linear acceleration. Aviation, Space, and Environmental Medicine, 77(2), 114−120.
120 Klokker, M., Vesterhauge, S., & Jansen, E. (2005). Pressure-equalizing earplugs do not prevent barotrauma on descent from 8000 ft cabin altitude. Aviation, Space, and Environmental Medicine, 76(11), 1079−1082. Kuhn, T. (1970). The structure of scientific revolutions (2nd ed.). Chicago: University of Chicago Press. Lawther, A., & Griffin, M. (1988). A survey of the occurrence of motion sickness amongst passengers at sea. Aviation, Space, and Environmental Medicine, 59, 399−406. Lingaas, E., & Midtvedt, T. (1987). The influence of high and low pressure on phagocytosis of Escherichia coli by human neutrophils in vitro. Aviation, Space and Environmental Medicine, 58, 1211−1214. Makinen, T., Rintamaki, H., Korpelainen, J., Kampman, V., Paakonen, T., Oksa, J., Palinkas, L., Leppaluoto, J., & Hassi, J. (2005). Postural sway during single and repeated cold exposures. Aviation, Space and Environmental Medicine, 76(10), 947−953. McKinley, R., Tripp, L., Jr, Bolia, S., & Roark, M. (2005). Computer modeling of acceleration effects on cerebral oxygen saturation. Aviation, Space, and Environmental Medicine, 76(8), 733−737.
D. Sredl Payne, S., & Chapell, M. (2005). Automated determination of bubble grades from Doppler ultrasound recordings. Aviation, Space and Environmental Medicine, 76(8), 771−777. Radtke, A., Popov, K., Bronstein, A., & Gresty, M. (2000). Evidence for a vestibulo-cardiac reflex in man. Lancet, 356, 736−737. Sredl, D. (1983). Airborne patient care management: A multidisciplinary approach. St. Louis: Medical Research Associates Publications. Thake, C., Mian, T., Garnham, A., & Mian, R. (2004). Leukocyte counts and neutrophil activity during 4 h of hypocapnic hypoxia equivalent to 4000m. Aviation, Space and Environmental Medicine, 75(9), 811−817. Wilson, G., Reis, G., & Tripp, L. (2005). EEG correlates of G-induced loss of consciousness. Aviation, Space and Environmental Medicine, 76(1), 19−27. Xiaojiang, X., Berglund, L., Cheuvroni, S., Endrusick, T., & Kolka, M. (2004). Model of human thermoregulation for intermittent regional cooling. Aviation, Space and Environmental Medicine, 75(12), 1065−1069. Yates, B., Aoki, M., Bronstein, A., & Gresty, M. (1999). Cardiovascular response to linear acceleration in humans. Experimental Brain Research, 125, 476−484.