G. Kaczmarczyk et al., VASOPRESSIN AND RENIN-ANGIOTENSIN MAINTAIN ARTERIAL-PRESSURE DURING PEEP IN NONEXPANDED, CONSCIOUS DOGS, American journal of physiology. Regulatory, integrative and comparative physiology, 40(5), 1996, pp. 1396-1402
Increases of plasma arginine vasopressin (AVP) and plasma renin activi
ty (PRA) during controlled mechanical ventilation (CMV) with positive
end-expiratory pressure (PEEP) induce positive fluid balances by decre
asing renal excretion. We investigated whether elevated levels of AVP
and/or PRA maintain mean arterial pressure (MAP) during PEEP under con
ditions where plasma volume is not expanded. Six conscious chronically
tracheotomized beagle dogs, kept under standardized conditions, were
investigated in four protocols. They were 1) control: 1 h spontaneous
breathing with a continuous positive airway pressure of 4 cmH(2)O (CPA
P 4) followed by 2 h CMV with PEEP, resulting in a mean airway pressur
e of similar to 20 cmH(2)O (%MV 20 referred to as ''PEEP''); 2)vasopre
ssin blockade: Ih CPAP 4, 2 h PEEP after intravenous application of an
AVP V-1-receptor antagonist (AVPA); 3) converting enzyme inhibition:
1 h CPAP 4, 2 h PEEP plus angiotensin-converting enzyme inhibition (AC
EI); and 4) combined blockade: 1 h CPAP 4, 2 h PEEP plus AVPA + ACEI.
In AVPA + ACEI, MAP decreased during PEEP from 101 +/- 4 to 75 +/- 10
mmHg, glomerular filtration rate (GFR) decreased from 3.6 +/- 0.3 to 1
.7 +/- 0.7 ml . min(-1). kg body wt(-1), heart rate increased from 95
+/- 10 to 122 +/- 7 beats/min, plasma aldosterone increased from 62 +/
- 26 to 353 +/- 63 pg/ml, plasma epinephrine increased from 81 +/- 15
to 352 +/- 89 pg/ml (all changes P < 0.05), and plasma norepinephrine
did not change. Neither MAP nor GFR changed during PEEP in control exp
eriments in which both PRA and AVP increased, in AVPA experiments in w
hich PRA increased, or in ACEI experiments in which AVP increased. We
conclude that both AVP and angiotensin II contribute to the maintenanc
e of MAP and GFR during PEEP. When both hormones are inhibited, no imm
ediate compensation exists to prevent an acute fall in MAP and GFR.