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Effect of tidal volume, intrathoracic pressure, and cardiac contractility on variations in pulse pressure, stroke volume, and intrathoracic blood volume.

ABSTRACT: We evaluated the impact of increasing tidal volume (V (t)), decreased chest wall compliance, and left ventricular (LV) contractility during intermittent positive-pressure ventilation (IPPV) on the relation between pulse pressure (PP) and LV stroke volume (SV(LV)) variation (PPV and SVV, respectively), and intrathoracic blood volume (ITBV) changes.Sixteen pentobarbital-anesthetized thoracotomized mongrel dogs were studied both before and after propranolol-induced acute ventricular failure (AVF) (n = 4), with and without chest and abdominal pneumatic binders to decrease chest wall compliance (n = 6), and during V (t) of 5, 10, 15, and 25 ml/kg (n = 6). SV(LV) and right ventricular stroke volume (SV(RV)) were derived from electromagnetic flow probes around aortic and pulmonary artery roots. Arterial pressure was measured in the aorta using a fluid-filled catheter. Arterial PPV and SVV were calculated over three breaths as (max - min)/[(max + min)/2]. ITBV changes during ventilation were inferred from the beat-to-beat volume differences between SV(RV) and SV(LV).Arterial PP and SV(LV) were tightly correlated during IPPV under all conditions (r (2) = 0.85). Both PPV and SVV increased progressively as V (t) increased and with thoraco-abdominal binding, and tended to decrease during AVF. SV(RV) phasically decreased during inspiration, whereas SV(LV) phasically decreased 2-3 beats later, such that ITBV decreased during inspiration and returned to apneic values during expiration. ITBV decrements increased with increasing V (t) or with thoraco-abdominal binding, and decreased during AVF owing to variations in SV(RV), such that both PPV and SVV tightly correlated with inspiration-associated changes in SV(RV) and ITBV.Arterial PP and SV(LV) are tightly correlated during IPPV and their relation is not altered by selective changes in LV contractility, intrathoracic pressure, or V (t). However, contractility, intrathoracic pressure, and V (t) directly alter the magnitude of PPV and SVV primarily by altering the inspiration-associated decreases in SV(RV) and ITBV.

SUBMITTER: Mesquida J

PROVIDER: S-EPMC3818902 | biostudies-literature | 2011 Oct

REPOSITORIES: biostudies-literature

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Effect of tidal volume, intrathoracic pressure, and cardiac contractility on variations in pulse pressure, stroke volume, and intrathoracic blood volume.

Mesquida Jaume J Kim Hyung Kook HK Pinsky Michael R MR

Intensive care medicine 20110708 10

<h4>Purpose</h4>We evaluated the impact of increasing tidal volume (V (t)), decreased chest wall compliance, and left ventricular (LV) contractility during intermittent positive-pressure ventilation (IPPV) on the relation between pulse pressure (PP) and LV stroke volume (SV(LV)) variation (PPV and SVV, respectively), and intrathoracic blood volume (ITBV) changes.<h4>Methods</h4>Sixteen pentobarbital-anesthetized thoracotomized mongrel dogs were studied both before and after propranolol-induced a ...[more]

PMID: 21739340

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Project description:The purpose of this study was to develop a method of estimating pulsatile ocular blood volume (POBV) from measurements taken during an ophthalmic exam, including axial length and using a tonometer capable of measuring intraocular pressure (IOP) and ocular pulse amplitude (OPA). Unpublished OPA data from a previous invasive study was used in the derivation, along with central corneal thickness (CCT) and axial length (AL), as well as IOP from the PASCAL dynamic contour tonometer (DCT) and intracameral (ICM) measurements of IOP for 60 cataract patients. Intracameral mean pressure was set to 15, 20, and 35 mmHg (randomized sequence) in the supine position, using a fluid-filled manometer. IOP and OPA measurements were acquired at each manometric setpoint (DCT and ICM simultaneously). In the current study, ocular rigidity (OR) was estimated using a published significant relationship of OR to the natural log of AL in which OR was invasively measured through fluid injection. Friedenwald's original pressure volume relationship was then used to derive the estimated POBV, delivered to the choroid with each heartbeat as a function of OR, systolic IOP (IOPsys), diastolic IOP (IOPdia), and OPA, according to the derived equation POBV = log (IOPsys/IOPdia) / OR. Linear regression analyses were performed comparing OPA to OR and calculated POBV at each of the three manometric setpoints. POBV was also compared to OPA/IOPdia with all data points combined. Significance threshold was p < 0.05. OR estimated from AL showed a significant positive relationship to OPA for both DCT (p < 0.011) and ICM (p < 0.006) at all three manometric pressure setpoints, with a greater slope for lower IOP. Calculated POBV also showed a significant positive relationship to OPA (p < 0.001) at all three setpoints with greater slope at lower IOP, and a significant negative relationship with IOPdia. In the combined analysis, POBV showed a significant positive relationship to OPA/ IOPdia (p < 0.001) in both ICM and DCT measurements with R2 = 0.9685, and R2 = 0.9589, respectively. POBV provides a straight-forward, clinically applicable method to estimate ocular blood supply noninvasively. Higher IOP in combination with lower OPA results in the lowest values of POBV. The simplified ratio, OPA/ IOPdia, may also provide a useful clinical tool for evaluating changes in ocular blood supply in diseases with a vascular component, such as diabetic retinopathy and normal tension glaucoma. Future studies are warranted.

Dataset Information

Effect of tidal volume, intrathoracic pressure, and cardiac contractility on variations in pulse pressure, stroke volume, and intrathoracic blood volume.

Publications

Effect of tidal volume, intrathoracic pressure, and cardiac contractility on variations in pulse pressure, stroke volume, and intrathoracic blood volume.

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