Valsalva maneuver
Forced expiratory effort against a closed glottis – P
pl
+ 30-50 mmHg.
5 phases:
1st. – at the onset of straining, the BP rises
2nd – a decrease of venous return, CO, BP; HR increases
3rd – reflex vasoconstriction – stop of the fall of BP, HR increases
4th – after the first inspirium, start of the breathing – decrease in BP –
- filling of the pulmonary circulation with blood
5th - an increase in BP – vasoconstricton persists, an excessive venous return – stimulation
of baroreceptors, causing bradycardia and a drop in BP to normal values.
Chemoreceptors
- peripheral
- central
Peripheral chemoreceptors:
Carotid and aortic bodies – near the carotid bifurcation, and the arch of the aorta.
The highest BF/g.
Stimulation – low PaO
2
(high PaCO
2
, acidosis)
Effects – an increasing of pressoric area of vasomotor centre, vasoconstriction (splanchnic),
redistribution of the blood, an increase in BP.
HR – primarily tachycardia, secondary bradycardia through baroreceptors
Central chemoreceptors: in the brain stem, on the ventral surface, H
+
zone.
Stimulation: a decrease in pH - acidosis.
Effects – changes in respiration, without any direct effect on cardiovascular system.
2) Nonspecific receptors
A) Trigeminal endings:
1) Oculocardiac reflex:
Stimulation:
pressure on the mechanoreceptors of eye and orbit –
Effects:
Depressoric effects on vessels and breathing - a decrease in
HR by 5-14 / min.
2) Kratschmer apnoeic reflex:
Stimulation:
Intranasal insufflation of various irritant gases (smoke,
ammonia ..)
Effects:
reflex respiratory arrest + laryngoconstriction + bradycardia
+ redistribution of the blood to the vital most important organs
(from the splanchnic circulation).
3) The diving reflex:
Stimulation
of the trigeminal region with cold (water).
Effects:
the same as in Kratschmer.
Oxygen conserving reflex – the changes primarily safeguard the blood and oxygen supply
of the heart, the brain.