Biomedical subjects

T J Heenan

Publications and source records attributed to T J Heenan.

3 recordsLinked to original sources

PubMed1981

Brain tissue pressure measurement during sodium nitroprusside infusion.

The effect of acute 25% decrease in mean arterial pressure (MAP) produced by sodium nitroprusside (SNP) infusion on mean intracerebral and cerebral perfusion pressures was examined in 7 swine with intracranial hypertension. All animals were anesthetized (alpha-chloralose), paralyzed (pancuronium bromide), orotracheally intubated and mechanically ventilated to maintain normocapnia. An epidural balloon was incrementally inflated to produce the desired brain tissue pressure (BTP) which was measured by an intracerebral microtransducer implanted contralateral to the balloon. MAP was measured from the carotid artery; cerebral perfusion pressure (CPP) was calculated as: MAP - BTP. During mildly (14 +/- 1 (SE) mm Hg) or moderately (37 +/- 3 mm Hg) increased BTP, SNP infusion increased BTP (17 +/- 1 and 44 +/- 3 mm Hg, respectively) (p less than 0.05). During severely increased BTP (70 +/- 4 mm Hg), SNP decreased BTP (53 +/- 4 mm Hg, p less than 0.05). Despite this variable BTP, CCP consistently decreased during SNP infusion. BTP and supratentorial subarachnoid cerebrospinal fluid pressure correlated closely; however, the supratentorial subarachnoid pressure consistently underestimated BTP. These findings suggest that estimation of BTP obtained from subarachnoid screw-type devices may not accurately record the pressure within cerebral tissue and the SBNP should not be administered to patients with known or suspected intracranial hypertension unless an intracranial (either BTP or subarachnoid) pressure is being monitored.

Animals↗

PubMed1981

Temporal responses of functional residual capacity and oxygen tension to changes in positive end-expiratory pressure.

PEEP is widely accepted as a therapy for some forms of acute respiratory failure (ARF). PEEP increases functional residual capacity (FRC), decreases intrapulmonary shunt fraction, and improves arterial oxygenation. The time required for FRC and arterial oxygen tension (PaO2) to stabilize after an adjustment in the level of PEEP is not clearly established. Therefore, to determine the temporal relationship between PEEP, FRC, and PaO2 after adjusting the level of PEEP, aspiration pneumonitis was produced in swine. The FRC and the PaO2 decreased within seconds after intratracheal instillation of 0.1 N HCl; FRC of all animals was restored to its control value after the application of PEEP, 5 cm H2O, but PaO2 remained low. It was necessary to increase PEEP to 20 cm H2O and FRC to twice the control value to return arterial oxygenation to control levels. After PEEP was applied, an average of 15 sec was required to increase FRC; the less compliant the lung, the more rapid the change. After PEEP was removed, FRC stabilized within an average of 22 sec. When PEEP, 25 cm H2O, was removed, arterial oxygenation decreased suddenly and substantially which suggests that PEEP, especially at higher levels, should not be discontinued, even momentarily, for nonessential maneuvers.

Animals↗

PubMed1980

Intermittent mandatory ventilation; is synchronization important?

Intermittent mandatory ventilation (IMV) allows patients to breathe spontaneously between mechanically supported breaths. Recently, several manufacturers have implied that nonsynchronous application of the mechanical breath may depress cardiovascular function and increase pulmonary barotrauma. Because it is technically difficult and expensive to synchronize mechanical ventilation to spontaneous breathing, we sought to determine whether there is any significant difference in cardiopulmonary function during synchronous and nonsynchronous mandatory ventilation. Our investigation failed to support the hypothesis that synchronization of spontaneous and mechanically mediated breathing is physiologically beneficial.

Airway Resistance↗