- Email: [email protected]
Response to Wilhelm and Roth
Biological Psychology 49 (1998) 221 – 222
Response
Response to Wilhelm and Roth David E. Anderson * Laboratory of Beha6ioral Sciences, Gerontology Research Center, National Institute on Aging/NIH, Baltimore, MD, USA
Wilhelm and Roth have succinctly described the main features of the ambulatory monitor of human respiration we developed in the late 1980s, discussed some of the limitations of this device, and outlined procedures that could improve its performance. With respect to the title of their critique, we would plead not guilty to the charge of ‘trusting too much’ that the digitized information in the microprocessor reflected a sinusoidal waveform of respiratory activity devoid of artifact. We were well aware from years of observation of polygraphic tracings of behaviorally-conditioned laboratory animals that analysis of respiration over time, even in the absence of postural artifact, can be a complex and daunting task. With regard to the substance of their critique, we would like to say a few words in defense of the monitor. First, to the extent that a breath occurs approximately every 4 s (i.e. 15 breaths per min), a 2 s electronic screen following each breath deletes approximately 50% of the possible artifact by definition. Second, screens that eliminate inductance shifts below and above the probable breathing range will eliminate another percentage of the artifact. Like Wilhelm and Roth, incidentally, we also concluded subsequent to our 1990 publication that the upper screen corresponding to 3 l of air intake was too high, and decreased it in later research. We are left, then, with movement artifact within the probable range of tidal volume, which could result in overestimation of the actual number of breaths per unit time. The individual difference in averaged breathing rates that we reported were spread across the normal range for healthy humans, including some at the lower end. The extent to which postural shifts in the range of tidal volume * Present address. Laboratory of Cardiovascular Science, National Institute on Aging, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA. Tel.: +1 410 5588213; fax: +1 410 5588233. 0301-0511/98/$ - see front matter Published by Elsevier Science B.V. PII S0301-0511(98)00037-4
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D.E. Anderson / Biological Psychology 49 (1998) 221–222
contributed to those breathing rates is an empirical question whose answer can be obtained only by systematic investigations such as those alluded to by Wilhelm and Roth. Our procedures for calibrating the system were based on the concept that breathing in the upright posture is thoracic and in the supine posture, abdominal. Wilhelm and Roth correctly point out that precise matching of the stretch/inductance ratios of the thoracic and abdominal bands is problematic, and their more extensive calibration procedures should improve estimations of the tidal volume, if not breathing frequency. Because of our ability to differentiate one subject from another on the basis of longitudinal breathing frequency records, and because of the apparent similarity of those findings to normative date in the literature, we offered our microprocessor as an advance over the technology existing at the time. Clearly, analyses of variability of interbreath intervals require a different approach than our averaging methodology, although it should be mentioned that others have continued to use and refine our monitor for more clinical concerns (Gorman, Papp, Martinez, et al., personal communication). In any event, we hope that Wilhelm and Roth (or others) will take the next steps to conduct the quantitative investigations that can reveal when and to what extent artifact within the range of tidal volume interferes with accurate monitoring of human ambulatory respiration, and then develop the technology to minimize it. We understand that this task will be formidable.
.
Response
Response to Wilhelm and Roth David E. Anderson * Laboratory of Beha6ioral Sciences, Gerontology Research Center, National Institute on Aging/NIH, Baltimore, MD, USA
Wilhelm and Roth have succinctly described the main features of the ambulatory monitor of human respiration we developed in the late 1980s, discussed some of the limitations of this device, and outlined procedures that could improve its performance. With respect to the title of their critique, we would plead not guilty to the charge of ‘trusting too much’ that the digitized information in the microprocessor reflected a sinusoidal waveform of respiratory activity devoid of artifact. We were well aware from years of observation of polygraphic tracings of behaviorally-conditioned laboratory animals that analysis of respiration over time, even in the absence of postural artifact, can be a complex and daunting task. With regard to the substance of their critique, we would like to say a few words in defense of the monitor. First, to the extent that a breath occurs approximately every 4 s (i.e. 15 breaths per min), a 2 s electronic screen following each breath deletes approximately 50% of the possible artifact by definition. Second, screens that eliminate inductance shifts below and above the probable breathing range will eliminate another percentage of the artifact. Like Wilhelm and Roth, incidentally, we also concluded subsequent to our 1990 publication that the upper screen corresponding to 3 l of air intake was too high, and decreased it in later research. We are left, then, with movement artifact within the probable range of tidal volume, which could result in overestimation of the actual number of breaths per unit time. The individual difference in averaged breathing rates that we reported were spread across the normal range for healthy humans, including some at the lower end. The extent to which postural shifts in the range of tidal volume * Present address. Laboratory of Cardiovascular Science, National Institute on Aging, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA. Tel.: +1 410 5588213; fax: +1 410 5588233. 0301-0511/98/$ - see front matter Published by Elsevier Science B.V. PII S0301-0511(98)00037-4
222
D.E. Anderson / Biological Psychology 49 (1998) 221–222
contributed to those breathing rates is an empirical question whose answer can be obtained only by systematic investigations such as those alluded to by Wilhelm and Roth. Our procedures for calibrating the system were based on the concept that breathing in the upright posture is thoracic and in the supine posture, abdominal. Wilhelm and Roth correctly point out that precise matching of the stretch/inductance ratios of the thoracic and abdominal bands is problematic, and their more extensive calibration procedures should improve estimations of the tidal volume, if not breathing frequency. Because of our ability to differentiate one subject from another on the basis of longitudinal breathing frequency records, and because of the apparent similarity of those findings to normative date in the literature, we offered our microprocessor as an advance over the technology existing at the time. Clearly, analyses of variability of interbreath intervals require a different approach than our averaging methodology, although it should be mentioned that others have continued to use and refine our monitor for more clinical concerns (Gorman, Papp, Martinez, et al., personal communication). In any event, we hope that Wilhelm and Roth (or others) will take the next steps to conduct the quantitative investigations that can reveal when and to what extent artifact within the range of tidal volume interferes with accurate monitoring of human ambulatory respiration, and then develop the technology to minimize it. We understand that this task will be formidable.
.