Pulmonary inflation reflex: Its lack of physiological significance in coronary circulation of humans

In awake dogs, voluntary deep inspiration results in a marked, reflex-mediated increase in coronary blood flow. To study this reflex in humans, we subselectively measured coronary blood flow velocity (CBFV) with a 3-F coronary Doppler catheter in 12 subjects with angiograpahically normal coronary arteries. In each subject, intracoronary papaverine increased CBFV to 4.8 ± 0.2 x resting CBFV and reduced coronary resistance to 0.20 ± 0.01 x resting coronary resistance, demonstrating normal vasodilator reserve in the vessel under study. Valsalva maneuver reduced CBFV to 0.67 ± 0.09 x resting CBFV and increased coronary resistance to 1.37 ± 0.20 x resting coronary resistance (P < 0.05 vs. control). Maximum voluntary inspiration, however, did not significantly change CBFV (peak response 1.03 ± 0.05 x resting CBFV) or coronary resistance (0.96 ± 0.04 x resting). To determine whether augmentation of resting α-adrenergic tone would potentiate the reflex, eight patients performed a sustained 33% maximal handgrip for 2 min. Maximal deep inspiration during handgrip failed to result in any significant change in CBFV or coronary resistance. These studies demonstrate that the canine pulmonary inflation reflex has little or no physiological significance in the coronary circulation of conscious humans. Additionally, these data suggest that the magnitude of reflex control of the coronary circulation may vary considerably between dogs and humans.