title: Ventilation is stimulated by small reductions in arterial pressure in the awake dog.
abstract: Changes in arterial pressure commonly accompany respiratory adaptations. The purpose of this study was to determine, in awake dogs (n = 6), the degree to which small acute decreases in arterial pressure affect ventilation and acid-base balance. Mean arterial pressure (MAP) was reduced by 6 +/- 2, 10 +/- 3, and 16 +/- 2% by intravenous infusion of sodium nitroprusside for sequential 20-min periods. In another experiment, the ventilatory response to hypercapnia was determined during MAP reduction of 16 +/- 3%. Step reductions in MAP were accompanied by increases in minute ventilation (maximum increase 152 +/- 75%) and step reductions in arterial PCO2 (PaCO2; maximum reduction -4.8 +/- 0.8 Torr). Although eupneic PaCO2 threshold was lowered during MAP reduction, ventilatory sensitivity to CO2 remained unchanged. Despite the lowered PaCO2, arterial [H+] remained constant (acid-base balance was maintained) as a result of a concurrent decrease in strong ion difference. Plasma renin activity increased during MAP reduction (93 +/- 39%) and may have contributed to the increase in minute ventilation, inasmuch as angiotensin II can stimulate respiration by a central mechanism. Evidence is provided that nitroprusside is unlikely to be a primary factor in these hypotensive responses. We conclude that relatively modest decreases in MAP have a consistent stimulatory effect on respiratory control. Therefore it is important to take into account effects of small changes in MAP when interpreting mechanisms for respiratory responses in awake animals.
authors.affiliation: Department of Physiology, Queen's University, Kingston, Ontario, Canada.
authors.forename: P J
authors.initials: PJ
authors.lastname: Ohtake
authors.forename: D B
authors.initials: DB
authors.lastname: Jennings
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000502:physiology*; D002245:Carbon Dioxide / Q000097:blood; D004285:Dogs; D006207:Half-Life; D006728:Hormones / Q000097:blood; D006935:Hypercapnia / Q000097:blood; D008297:Male; D009599:Nitroprusside / Q000494:pharmacology; D009994:Osmolar Concentration; D010101:Oxygen Consumption / Q000502:physiology; D012083:Renin / Q000097:blood; D015656:Respiratory Mechanics / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000502:physiology
chemical_list: D006728:Hormones; D000804:Angiotensin II; D001127:Arginine Vasopressin; D002245:Carbon Dioxide; D009599:Nitroprusside; D012083:Renin