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Wrapping of aortic aneurysm
LETTERS
would be approximately 1.3 ml 02/100 ml of blood flow (a 29 percent rather than a 38.5 percent increase). In addition, for any given mixed venous POz, the lower the oxygen-carrying capacity of the blood, the smaller is the achievable arteriovenous oxygen difference. As a result of these combined effects, decreases in blood oxygen-carrying capacity tend to offset the benefits of increases in Psc. The mixing technique2 used by Schrumpf et al. for determination of Pso adequately defines the position of the hemoglobin-oxygen equilibrium for a given oxygen tension but does not quantitate the blood’s oxygen-carrying capacity. Thus, the study demonstrates an increase in P50 with propranolol therapy but does not consider the possibility that the drug might also reduce the maximal volume of oxygen that can be bound to each gram of measurable hemoglobin. This possibility can be excluded by direct measurement of the oxygen content of an aliquot of fully oxygenated blood. The conclusion that P50 increased during propranolol therapy seems valid. However, any consideration of changes in oxygen delivery resulting from increases in P50 should include the effect of possible changes in oxygen-carrying capacity. The argument that propranolol may enhance systemic oxygen delivery would have been strengthened by demonstrating that the drug does not alter the blood’s oxygencarrying capacity.
WRAPPING
OF AORTIC ANEURYSM
Kolff et a1.l present a method of handling aneurysm of the aortic arch. The technique consists of wrapping the dilated arch with Dacron graft, a method described by us in January 19712 and successfully applied by us in more than 80 patients. Sorry to say, this fact was entirely disregarded by the authors. Figure 1 shows, at top, an illustration from our 1976 article3 and, at bottom, Figure 3 of the article by Kolff et al. Francis Robicsek, MD Department of Thoracic and Cardiovascular Surgery Charlotte Memorial Hospital Charlotte, North Carolina References
Bates
1. Kofff J, RJ, Bafderman C, et al: Acute atiic arch dissection: reevaluation of the lndicatlons for medlcal and surgical therapy. Am J Cardiol 39~727-733, 1978 2. Robksek F, Daugherty HK, Mullen DC: External grafting of aortic aneurysm. J Thorac Cardiovasc Surg 61:131-134, 1971 3. Robfcsek F, Daugherty HK, Mullen DC, et al: Long-range observations with external acwtlc grafts. J Cardlovasc Surg 17:195-201. 1976
CAPT Stephen H. Humphrey, MD MAJ Barry R. Alter, MD Cardiology Service Department of internal Medicine Brooke Army Medical Center Fort Sam Houston, Texas References 1. Schrumpf JD, Shepa long-term propranolol 40:76-82.1977 2. Edwardr M, Martfn R: affect. J Appl physiol
DS, Woffson S, et al: Altered hemoglobin-oxygen affinity with therapy in patients with coronary artery disease. Am J Cardiol Mixing technique for tlm oxygewhamoglobin 21:1898-1902. 1966
equilibrium and Bohr
REPLY
Humphrey and Alter have made a valid point that the oxygen carrying capacity of the blood is a critical determinant of oxygen delivery to tissues. However, our study demonstrated no change in either hemoglobin or hematocrit consequent to propranolol administration. To turn their conclusion around, it has not been demonstrated that propranolol does alter the blood’s oxygen-carrying capacity. In any event, as concluded in our report, the precise increase in oxygen delivery produced by propranolol cannot really be calculated. The change would be different at the usual low PO2 of coronary sinus blood compared with the peripheral vein blood analyzed in our study. There is a gradient of POz from subepicardium to suhendocardium, and coronary atherosclerosis itself is a heterogenous disease. Therefore, we concluded that “at any tissue PO2 level, there would be some increase in oxygen unloading. . . . the measurable effects of such a shift would be difficult to predict.” Steven Wolfson, MD, FACC Lawrence S. Cohen, MD, FACC Cardiology Section Yale University School of Medicine New Haven, Connecticut
792
April 1979
The American Journal of CARDIDLDGY
FtGUKE 1. Top, illustration of method of wrapping dilated aoftic arch as repwted by Robicsak et al. in 19763 (reprinted by permlsslon). Sottom, illustration from article by Kolff et al.’
Volume 41
would be approximately 1.3 ml 02/100 ml of blood flow (a 29 percent rather than a 38.5 percent increase). In addition, for any given mixed venous POz, the lower the oxygen-carrying capacity of the blood, the smaller is the achievable arteriovenous oxygen difference. As a result of these combined effects, decreases in blood oxygen-carrying capacity tend to offset the benefits of increases in Psc. The mixing technique2 used by Schrumpf et al. for determination of Pso adequately defines the position of the hemoglobin-oxygen equilibrium for a given oxygen tension but does not quantitate the blood’s oxygen-carrying capacity. Thus, the study demonstrates an increase in P50 with propranolol therapy but does not consider the possibility that the drug might also reduce the maximal volume of oxygen that can be bound to each gram of measurable hemoglobin. This possibility can be excluded by direct measurement of the oxygen content of an aliquot of fully oxygenated blood. The conclusion that P50 increased during propranolol therapy seems valid. However, any consideration of changes in oxygen delivery resulting from increases in P50 should include the effect of possible changes in oxygen-carrying capacity. The argument that propranolol may enhance systemic oxygen delivery would have been strengthened by demonstrating that the drug does not alter the blood’s oxygencarrying capacity.
WRAPPING
OF AORTIC ANEURYSM
Kolff et a1.l present a method of handling aneurysm of the aortic arch. The technique consists of wrapping the dilated arch with Dacron graft, a method described by us in January 19712 and successfully applied by us in more than 80 patients. Sorry to say, this fact was entirely disregarded by the authors. Figure 1 shows, at top, an illustration from our 1976 article3 and, at bottom, Figure 3 of the article by Kolff et al. Francis Robicsek, MD Department of Thoracic and Cardiovascular Surgery Charlotte Memorial Hospital Charlotte, North Carolina References
Bates
1. Kofff J, RJ, Bafderman C, et al: Acute atiic arch dissection: reevaluation of the lndicatlons for medlcal and surgical therapy. Am J Cardiol 39~727-733, 1978 2. Robksek F, Daugherty HK, Mullen DC: External grafting of aortic aneurysm. J Thorac Cardiovasc Surg 61:131-134, 1971 3. Robfcsek F, Daugherty HK, Mullen DC, et al: Long-range observations with external acwtlc grafts. J Cardlovasc Surg 17:195-201. 1976
CAPT Stephen H. Humphrey, MD MAJ Barry R. Alter, MD Cardiology Service Department of internal Medicine Brooke Army Medical Center Fort Sam Houston, Texas References 1. Schrumpf JD, Shepa long-term propranolol 40:76-82.1977 2. Edwardr M, Martfn R: affect. J Appl physiol
DS, Woffson S, et al: Altered hemoglobin-oxygen affinity with therapy in patients with coronary artery disease. Am J Cardiol Mixing technique for tlm oxygewhamoglobin 21:1898-1902. 1966
equilibrium and Bohr
REPLY
Humphrey and Alter have made a valid point that the oxygen carrying capacity of the blood is a critical determinant of oxygen delivery to tissues. However, our study demonstrated no change in either hemoglobin or hematocrit consequent to propranolol administration. To turn their conclusion around, it has not been demonstrated that propranolol does alter the blood’s oxygen-carrying capacity. In any event, as concluded in our report, the precise increase in oxygen delivery produced by propranolol cannot really be calculated. The change would be different at the usual low PO2 of coronary sinus blood compared with the peripheral vein blood analyzed in our study. There is a gradient of POz from subepicardium to suhendocardium, and coronary atherosclerosis itself is a heterogenous disease. Therefore, we concluded that “at any tissue PO2 level, there would be some increase in oxygen unloading. . . . the measurable effects of such a shift would be difficult to predict.” Steven Wolfson, MD, FACC Lawrence S. Cohen, MD, FACC Cardiology Section Yale University School of Medicine New Haven, Connecticut
792
April 1979
The American Journal of CARDIDLDGY
FtGUKE 1. Top, illustration of method of wrapping dilated aoftic arch as repwted by Robicsak et al. in 19763 (reprinted by permlsslon). Sottom, illustration from article by Kolff et al.’
Volume 41