CARDIOPULMONARY RESPONSES TO EXERCISE IN PATIENTS WITH HYPERTROPHIC CARDIOMYOPATHY

Objective-To examine the submaximal and maximal indices of the exercis e response of patients with hypertrophic cardiomyopathy. Design and se tting-Prospective examination of cardiopulmonary responses to ramp exe rcise test of a consecutive group of patients with hypertrophic cardio myopathy attending a cardiomyopathy outpatient clinic. Methods-50 pati ents aged 12 to 76 years (mean (SD) 35 (14)) with diagnosis of hypertr ophic cardiomyopathy performed incremental cycle ergometry; 22 sedenta ry volunteers (seven female, 15 male) aged 14 to 58 years (mean (SD) 3 1 (12)) served as controls. Respiratory gas was continuously sampled f rom the mouthpiece, and its concentration profile phase aligned to the respired air flow signals. Following analogue to digital conversion, gas exchange variables were computed breath by breath and the data wer e averaged every 30 seconds for graphic display. A 12 lead ECG was mon itored continuously and recorded every three minutes during the exerci se. Results-Both the peak oxygen uptake attained on the test ((V) over dot o(2), peak) and anaerobic threshold were reduced in patients with hypertrophic cardiomyopathy compared with the control group (p < 0.00 01). In 29 patients (59%) the (V) over dot o(2), peak was less than 60 % and only two patients achieved a peak above 80% of their predicted v alues. The anaerobic threshold was below 60% of the predicted value in 31 patients and above 80% in only three patients. The slope of oxygen uptake/ work rate relation (Delta(V) over dot o(2)/Delta WR) was decr eased in 16 patients (32%). The maximum oxygen pulse ((V) over dot o(2 )/HR) was reduced as a percentage of the predicted value, and became f lat at high work rates in 32 patients. There was a significant correla tion between anaerobic threshold and (V) over dot o(2) peak (p < 0.000 1), work efficiency (p < 0.0001), and maximum oxygen pulse (p < 0.0001 ). The slope of change in ventilation against change in carbon dioxide output (Delta(V) over dot is an element of/Delta(V) over dot CO2) for the subanaerobic threshold range was increased in 36 patients (72%) a nd was inversely correlated with anaerobic threshold (p < 0.0002). Con clusions-There were severe abnormalities in maximal and submaximal ind ices of pulmonary gas exchange in a cohort of hypertrophic cardiomyopa thy patients attending a referral cardiovascular clinic. The pattern o f the abnormalities suggests that a reduced stroke volume response, ve ntilation/perfusion mismatch, and abnormal peripheral oxygen utilisati on are the possible mechanisms of exercise intolerance.