Retinal, Choroidal and Total Ocular Blood Flow Response to Hypercarbia during Spontaneous Breathing and Mechanical Ventilation

Abstract

The effect of hypercarbia on ocular blood flow was studied in the newborn piglet with the isotope-labeled microsphere method. Blood flow measurements were made during spontaneous breathing and during paralyzation (pancuronium) and mechanical ventilation. Retinal blood flow increased from 0.40 ± 0.07 (mean ± SEM) ml/min/g at baseline levels to 0.91 ± 0.17 ml/min/g at a PaCO₂ level of 11.0 kPa during spontaneous ventilation. A similar response was observed during paralyzation and mechanical ventilation (0.89 ± 0.15 ml/ min/g at a PaCO₂ of 11.1 kPa). For choroidal blood flow, however, the increase caused by hypercarbia during spontaneous ventilation (16.14 ± 3.69 to 29.15 ± 3.22 ml/min/g) was significantly reduced when the animals were paralyzed and mechanically ventilated (15.99 ± 2.99 to 23.51 ± 3.41 ml/min/g). Since choroidal blood flow accounts for 60–80% of oxygen delivery to the retina, paralyzation and mechanical ventilation may significantly reduce oxygen delivery to the retina during hypercarbia.

Blood flow velocity response of the ophthalmic artery and anterior optic nerve head capillaries to carbogen gas in the rhesus monkey model of optic nerve head ischemia

“…A reduction of up to 80% in oxygen delivery to the retina is possible. 47 We were not able to detect significant carbogen-induced alterations in the ophthalmic artery and ONH microcirculations with CDI and CSLF. The large differences in adjusted values may have been influenced by marked differences in HRF values between the ET OS control eyes and the higher Sham OS nontreated control eyes.…”

“…The response to hypercapnia of the choroidal circulation is reduced when animals are paralyzed compared to spontaneous breathing. A reduction of up to 80% in oxygen delivery to the retina is possible 47 …”

Retinal and Choroidal Blood Flow Response to Hyperoxemia after Severe Hypoxemia in the Newborn Piglet

“…Both pentobarbital and pancuronium are known to influence CBF [20,21], and studies indicate that pancuronium might affect ChBF during hypercapnia [22], It can therefore not be excluded that both these drugs may have affected the results obtained.…”