EVALUATION OF PULSATILE AND NONPULSATILE FLOW IN CAPILLARIES OF GOAT SKELETAL-MUSCLE USING INTRAVITAL MICROSCOPY

It is commonly believed that pulsatile how generated by the pumping ac tion of the heart is dampened out by the time it reaches the microcirc ulation. In clinical practice, most of the cardiopulmonary bypass pump s and ventricular assist devices are nonpulsatile. To test the hypothe sis that pulsatile flow generated by the heart does exist at the micro vascular level, intravital microscopy of a large animal model (goat) w as developed to visualize and to videorecord the surface microcirculat ion of the flexor carpi ulnaris muscle from the right forelimb. Densit y of perfused capillaries and red blood cell velocity in capillaries w ere measured in five goats during pulsatile perfusion provided by the heart and during a subsequent 3-hr period of nonpulsatile perfusion pr ovided by a centrifugal ventricular assist device (Centrimed, Sarns 3M ) that bypassed the heart. Throughout the experiment, the heart rate, innominate artery mean blood pressure, and flow remained unchanged. Du ring the pulsatile regimen, velocities showed regular fluctuations tha t coincided with the period of the cardiac cycle (range of periods: 0. 5-0.8 sec). The peak velocity amplitudes (range: 0.25-0.55 mm/sec) cor related directly with the amplitude of the pulse pressure. During the nonpulsatile regimen, no such correlations were seen. During pulsatile flow and during the 3-hr nonpulsatile period, capillary density remai ned stable at 24 capillaries/mm of test line but there were significan t increases in red cell velocity, from 0.8 to 1.2 mm/sec (P < 0.05), a nd in coefficient of variation of velocity (used as an index of how he terogeneity), from 19 to 34% (P < 0.05). We conclude that (1) pulsatil ity exists in the capillary bed and that it directly correlates with t he pumping action of the heart and (2) nonpulsatile flow produced by t he ventricular assist device does not cause an acute deterioration in microvascular perfusion. We interpret the increase in heterogeneity of how as an early sign of microvascular dysfunction. Prolonged use of t he nonpulsatile device may, therefore, lead to deterioration in perfus ion that could compromize the function of the organ. (C) 1994 Academic Press, Inc,