EFFECT OF VASOACTIVE INTESTINAL POLYPEPTIDE (VIP) ON PULMONARY VENTILATION-PERFUSION RELATIONSHIPS AND CENTRAL HEMODYNAMICS IN HEALTHY-SUBJECTS

Ventilation-perfusion relationships of the lung (VA/Q) and central hae modynamics were studied in nine healthy subjects before and during 30 min of vasoactive intestinal polypeptide (VIP) infusion (20 ng kg.min- 1). During the infusion, arterial concentrations of VIP rose from 16.1 +/- 6.1 to 420 +/- 110 pmol l-1 and noradrenaline concentrations doub led (P < 0.01). VA/Q distributions, determined by inert gas eliminatio n technique, were significantly shifted to lower values for VA/Q with slight increases in dispersions, but arterial oxygen tension remained unchanged. Heart rate, stroke volume and cardiac output rose 27, 44 an d 80% respectively (P < 0.01). Systematic arterial pressure stabilized at a slightly lower level compared to basal (base line: 93 +/- 5 mmHg , VIP: 88 +/- 6 mmHg, P < 0.05). Right atrial and pulmonary capillary wedge pressures remained unchanged during VIP infusion, while pulmonar y vascular resistance and systematic vascular resistance decreased sig nificantly, by 25% (P < 0.03) and 53% (P < 0.01), respectively. It is concluded that VIP causes: (1) alterations in ventilation-perfusion di stributions, but generates no shunt and does not cause hypoxaemia duri ng 30 min infusion, (2) reduction of pulmonary and systemic vascular r esistances and afterload reduction of the left ventricle, (3) reflex s ympathoadrenal stimulation with increasing heart rate and myocardial c ontractility, and (4) a direct positive inotropic effect on the myocar dium.