No abstract

In 13 canine hearts, 158 disappearance curves for 133 Xe and antipyrine-125 I, given by intra-arterial slug injection, were recorded at a wide range of perfusion rates. Flow rates (ml/100 g/min) calculated from these curves by a variety of methods were compared with measured flow rates (F a ) per weight of perfused tissue. Perfusion of isolated, supported hearts and of anterior descending coronary arteries in open-chest dogs provided similar data. The semilogarithmic slope of curves from apex or whole heart decreased with time, particularly at high flow rates. There was a small, consistent difference in shape between antipyrine and xenon curves, suggesting that radioactivity in fat contributed somewhat to this tailing. Estimation of flow rate from the steepest semilog slope yielded an average value of 1.1F a for all rates; estimation from slope at 30% of peak radioactivity gave 0.9F a . The curves were closely described by a two-exponential equation which gave flow estimates of 0.95F a when collimation limited the observations to the heart apex, and lower values when the whole heart was observed. Peak height/area methods gave values of approximately 0.75F a in spite of various compensations for the impossibility of recording the curve until radioactivity = 0. Additional Key Wordsdiffusible indicators; capillary exchange; coronary blood flow; circulatory transport functions; xenon; indicator dilution; radioisotopes; antipyrine; dog; myocardial exchange; flow methodology A wide variety of methods for estimation of tissue blood flow rate from indicator washout curves have evolved (1-4), differing in choice of indicator and in method of analysis. All assume steady flow, and some assume continuous diffusion equilibria between capillary blood and tissues. This latter assumption is reasonable for highly diffusible indicators (heat, water, xenon) at low flow rates through well-perfused organs lacking arteriovenous anastomoses because, under these conditions, diffusional exchanges will be rapid compared to removal from the tissue by convective transport of blood in the capillaries. It is also clear that if the diffusion distances between capillaries are large and the capillary transit times are Dr. Bassingthwaighte is the recipient of a National Institutes of Health Career Development Award. Dr. Strandell is the recipient of a National Institutes of Health Fellowship Award (1-FO-5-TW-894). Dr. Strandell present address is The Roslagstull Hospital, Stockholm, Sweden.This report was read at the meeting of the American Federation for Clinical Research, Chicago, November 4, 1966. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript short and the flow is rapid, diffusion gradients will exist and will be large for the less readily diffusible substances.It is the purpose of this report to show that there is little apparent diffusion limitation for the washout of the highly diffusible indicators, water-soluble antipyrine and lipid-soluble xenon, from the perfused hearts of dogs...

The circulatory function in normal young adults has been studied by heart catheterization both at rest and during exercise. The reports include both ordinarily trained individuals and athletes (for references see 5, 6, 17, 37). Elderly subects, however, have not previously been studied by this technique, but by dye dilution the cardiac output and stroke volume at rest in elderly subjects were found to be lower than in young adults (7).The present study formed part of a more detailed investigation of the circulatory function in old men (30-35). Besides, it was found necessary to collect catheterization data for healthy elderly subjects as the central circulation is nowadays studied for diagnostic reasons in an increasing number of elderly patients. Because most routine catheterizations are performed in supine and most studies on exercise physiology in sitting position, the subjects were studied in both positions. A preliminary report has been issued on the findings concerning the first subjects studied (14).

STRANDELL, T. Heart rate, arterial lactate concentration and oxygen uptake during exercise in old men compared with young men. Acta physiol. scand. 1964. 60. 197-216. -In 121 healthy men aged 30-83 years heart rate, oxygen uptake, arterial lactate and pyruvate concentrations were studied during stepwise increased work loads on a bicycle ergometer. The relationship between heart rate and work load was not affected by age but the final heart rate and work load decreased with age. I n the younger ages the most usual reason for breaking off the test was fatigue in the legs, in the higher ages dyspnoea. The regression line for log lactate on heart rate during exercise was on a higher level in old men than in young. Blood lactate during exercise was correlated both to the degree of circulatory steady state, the heart rate, and the final work load irrespective of age. The relationship between lactate and excess lactate during exercise was similar in old and young men, excess lactate being equivalent to lactate reduced by 2 mM/1. In 20 men aged 60-83 years there was a t 600 kpmlmin a negative correlation between mechanical efficiency and heart rate and a positive between oxygen uptake and weight or heart rate. No correlation was found between oxygen uptake or mechanical efficiency and age, degree of circulatory steady state or blood lactate concentration.With increasing average life span of the population the knowledge of normal physiology in higher age groups becomes more and more important. Studies of exercise physiology in man in different age groups are, however, not very numerous and mostly concern subjects below 60 years of age.The maximal oxygen uptake and maximal heart rate have been found to decline with rising age both in cross-sectional (Robinson 1938, Valentin et al. 1955, Astrand 1958, Konig et al. 1961, Hollman 1963 and longitudinal studies (Dill, Horwath and Craig 1958) and irrespective of whether the exercise has been performed on a treadmill or a bicycle ergometer. From 30 to 60 years of age the mean decline in the maximal oxygen uptake amounts in men to approximately 25-30 per cent. The maximal heart rate during exercise inlthe 197 13-643015. Acfn physiol. scand. Vol. 60.