Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PRESSURE”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 469 records · Page 26Linked to original sources
PubMedDate not supplied

Comparison between casual blood pressure and ambulatory blood pressure monitoring parameters in healthy and hypertensive adolescents.

Casual blood pressure measurements were compared with mean ambulatory blood pressure values during wakefulness and sleep in 45 normotensive and 30 hypertensive adolescents of both sexes aged 10-18 years. Two sets of auscultatory casual blood pressure were obtained, one in a pediatric office setting (office blood pressure), performed by the physician, and one in the ambulatory blood pressure monitoring (ABPM) unit, performed by a trained nurse, prior to the initiation of ABPM (pre-ABPM blood pressure). In normotensive and hypertensive subjects of both sexes, the mean office systolic blood pressure (SBP) was lower than the mean pre-ABPM SBP, and the mean office diastolic blood pressure (DBP) was lower than the mean pre-ABPM DBP. In normotensive participants, the mean pre-ABPM SBP/DBP was lower than the mean ABPM SBP/DBP while awake, the mean ABPM SBP/DBP during sleep being lower than the mean ABPM SBP/DBP values while awake and the mean pre-ABPM SBP/DBP. No statistical difference was demonstrated between the mean office SBP and the mean ABPM SBP during sleep, the mean ABPM DBP during sleep being lower than the mean office DBP. The hypertensive adolescents presented a blood pressure profile similar to that of the normotensive group, albeit shifted upwards, with no significant difference between the mean pre-ABPM SBP and the mean ABPM SBP while awake but a higher mean pre-ABPM DBP than mean ABPM DBP while awake. This study suggests that, by evaluating the casual blood pressure in different environment/observer situations, the power of casual blood pressure to predict inadequate blood pressure control, manifested as abnormal ABPM parameters, can be enhanced. Our data indicate ABPM to be the method of choice for the early diagnosis and adequate follow-up of adolescent hypertension.

Adolescent↗
PubMed2007

Blind identification of the aortic pressure waveform from multiple peripheral artery pressure waveforms.

We have developed a new technique to estimate the clinically relevant aortic pressure waveform from multiple, less invasively measured peripheral artery pressure waveforms. The technique is based on multichannel blind system identification in which two or more measured outputs (peripheral artery pressure waveforms) of a single-input, multi-output system (arterial tree) are mathematically analyzed so as to reconstruct the common unobserved input (aortic pressure waveform) to within an arbitrary scale factor. The technique then invokes Poiseuille's law to calibrate the reconstructed waveform to absolute pressure. Consequently, in contrast to previous related efforts, the technique does not utilize a generalized transfer function or any training data and is therefore entirely patient and time specific. To demonstrate proof of concept, we have evaluated the technique with respect to four swine in which peripheral artery pressure waveforms from the femoral and radial arteries and a reference aortic pressure waveform from the descending thoracic aorta were simultaneously measured during diverse hemodynamic interventions. We report that the technique reliably estimated the entire aortic pressure waveform with an overall root mean squared error (RMSE) of 4.6 mmHg. For comparison, the average overall RMSE between the peripheral artery pressure and reference aortic pressure waveforms was 8.6 mmHg. Thus the technique reduced the RMSE by 47%. As a result, the technique also provided similar improvements in the estimation of systolic pressure, pulse pressure, and the ejection interval. With further successful testing, the technique may ultimately be employed for more precise monitoring and titration of therapy in, for example, critically ill and hypertension patients.

Algorithms↗
PubMed1988

Wideband external pulse recording during cuff deflation: a new technique for evaluation of the arterial pressure pulse and measurement of blood pressure.

Analysis of the external brachial pulse recorded during standard blood pressure cuff deflation with use of a transducer with a wide frequency response has revealed a reproducible pattern with three distinct components that we have labeled K1, K2, and K3. K1 is a low-amplitude, low-frequency signal that is present with cuff pressures above systolic pressure. K2 is a triphasic signal appearing at systolic pressure and disappearing at diastolic pressure, which approximately corresponds to the audible Korotkoff sound. K3 appears with cuff pressure between systolic and diastolic pressure and continues to be present below diastolic pressure. Intra-arterial pressure recordings made with a high-fidelity Millar catheter-tip manometer revealed K2 and K3 analogs. K3 resembles the intra-arterial pressure waveform and when calibrated according to the pulse pressure, noninvasive dK3/dt determinations correlated well with intra-arterial dP/dt measurements. The appearance/disappearance property of K2 was designated as the "K2 algorithm" and represents a new, objective noninvasive method for measurement of blood pressure. The K2 algorithm compares favorably with intra-arterial measurements, is more accurate than the auscultatory technique, and may be especially useful in clinical situations in which the auscultatory technique does not work well.

Adolescent↗
PubMed2007

Elevations in renal interstitial hydrostatic pressure and 20-hydroxyeicosatetraenoic acid contribute to pressure natriuresis.

This study examined the role of changes in renal interstitial pressure on the renal levels of cytochrome P450 metabolites of arachidonic acid and compared the effects of inhibition of the formation of 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids with 1-aminobenzotriazole on the pressure-natriuretic response versus that seen after administration of HET0016, a more selective inhibitor of the formation of 20-HETE. Renal interstitial pressure rose by 3.4+/-0.3 mm Hg, and the levels of 20-HETE in renal cortical tissue doubled when renal perfusion pressure was increased from 100 to 160 mm Hg. Removal of the renal capsule prevented the increase in renal interstitial pressure and 20-HETE levels after an elevation in renal perfusion pressure. Urine flow and sodium excretion increased 5-fold when renal perfusion pressure was increased from 106 to 160 mm Hg. The administration of 1-aminobenzotriazole (50 mg/kg, IP) or HET0016 (10 mg/kg IV bolus plus 1 mg/kg per hour of infusion) decreased the pressure-natriuretic response by 50% and inhibited the renal formation of 20-HETE and epoxyeicosatrienoic acids by 90% and 50%, respectively. Administration of a lower dose of HET0016 (1 mg/kg per hour, IV) selectively reduced the formation of 20-HETE by 80% without inhibiting renal epoxygenase activity and blunted the pressure-natriuretic response by 42%. These results indicate that elevations in renal perfusion pressure increase 20-HETE levels in the kidney secondary to a rise in renal interstitial pressure. They also suggest that 20-HETE, rather than epoxyeicosatrienoic acids, modulates the pressure-natriuretic response, because selective blockade of the formation of 20-HETE with HET0016 blunts the response to the same extent as that seen after inhibition of the formation of 20-HETE and epoxyeicosatrienoic acids with 1-aminobenzotriazole.

Amidines↗
PubMed1992

Pressure natriuresis. Role of renal interstitial hydrostatic pressure.

The kidneys play a major role in the long-term regulation of extracellular fluid volume and arterial pressure. A central component of the feedback system for long-term control of arterial pressure is the pressure-natriuresis mechanism, whereby increases in renal perfusion pressure lead to decreases in sodium reabsorption and increases in sodium excretion. The specific intrarenal mechanism for the decrease in tubular reabsorption in response to increases in renal perfusion pressure appears to be related to increases in renal interstitial hydrostatic pressure (RIHP). Increases in renal perfusion pressure are associated with significant increases in RIHP. The mechanism whereby RIHP increases in the absence of discernible changes in whole kidney renal blood flow and peritubular capillary hydrostatic and/or oncotic pressures may be related to alterations in renal medullary hemodynamics. Several lines of investigation support an important quantitative role for RIHP in mediating pressure natriuresis. Preventing RIHP from increasing in response to increases in renal perfusion pressure markedly attenuates pressure natriuresis. Furthermore, direct increases in RIHP, comparable to increases measured in response to increases in renal perfusion pressure, have been shown to significantly decrease tubular reabsorption of sodium in the proximal tubule and increase sodium excretion. The exact mechanism whereby RIHP influences tubular reabsorption is unknown but may be related to alterations in tight junctional permeability to sodium in proximal tubules and/or release of renal autacoids such as prostaglandins.

Animals↗
PubMed1992

Influence of short-term blood pressure variability on blood pressure determinations.

To evaluate the effect of blood pressure variability on Riva Rocci Korotkoff blood pressure determinations, we studied the intra-arterial pressure during Riva Rocci Korotkoff determinations in 25 patients. In 50 measurements with a cuff deflation rate of 2.5 mm Hg/sec, the systolic intra-arterial pressure at Korotkoff phase 1 was 2.1 (95% confidence interval 1.2-3.0) mm Hg higher than the average systolic intra-arterial pressure in the 20 seconds surrounding this moment (p less than 0.01). This elevation was shown to increase with increasing blood pressure variability, as expressed by the standard deviation of the systolic blood pressure. The elevation caused by the proposed mechanism was amplified when a slow cuff deflation rate of 1.5 mm Hg/sec was used. No significant difference was noted in the diastolic intra-arterial pressure at Korotkoff phase 5, when a normal deflation rate of 2.5 mm Hg/sec was used. A slow cuff deflation rate caused a small elevation in diastolic pressure at the moment of Korotkoff phase 5. We conclude that even normally occurring blood pressure variability might lead to a consistent elevation of systolic Riva Rocci Korotkoff blood pressure measurements. This effect is reinforced by an increasing blood pressure variability and by a slower cuff deflation rate.

Aged↗
PubMed1997

Pressure gradients affecting the labyrinth during hypobaric pressure. Experimental study.

Hypobaric effects on the perilymph pressure were investigated in 18 cats. The perilymph, tympanic cavity, cerebrospinal fluid, and systemic and ambient pressure changes were continuously recorded relative to the atmospheric pressure. The pressure equilibration of the eustachian tube and the cochlear aqueduct was studied, as well as the effects of blocking these channels. During ascent, the physiologic opening of the eustachian tube reduced the pressure gradients across the tympanic membrane. The patent cochlear aqueduct equilibrated perilymph pressure to cerebrospinal fluid compartment levels with a considerable pressure gradient across the oval and round windows. With the aqueduct blocked, the pressure decrease within the labyrinth and tympanic cavities was limited, resulting in large pressure gradients toward the chamber and the cerebrospinal fluid compartments, respectively. We conclude that closed cavities with limited pressure release capacities are the cause of the pressure gradients. The strain exerted by these pressure gradients is potentially harmful to the ear.

Animals↗
PubMed1995

A comparative evaluation of pressure-triggering and flow-triggering in pressure support ventilation (PSV) for neonates using an animal model.

The triggering system in pressure support ventilation needs to respond rapidly, especially in neonates. The aim of this study was to compare the effects of flow-triggered and pressure-triggered pressure support ventilation on neonatal mechanical ventilation using an animal model. Respiratory flow, airway pressure, oesophageal pressure, and diaphragmatic electromyogram were measured during pressure support ventilation in five anaesthetized rabbits. The animals were connected to a VIPBIRD (Bird, U.S.A.) (CPAP mode, pressure support ventilation, 5 cm H2O and PEEP 0 cm H2O). Flow-triggering sensitivity was set at 0.2l/min, 0.5l/min, 1.01l/min, or 1.5l/min. Pressure-triggering sensitivity was set at -1.0 cm H2O. Shorter trigger delay and longer pressure support time were observed in flow-triggering. There was also less diaphragmatic activity in flow-triggering as evidenced by the amplitude of integrated diaphragmatic electromyogram and negative deflection of oesophageal pressure. The findings suggest that flow-triggering will prove superior to pressure-triggering in pressure support ventilation for neonates.

Animals↗
PubMed2002

Blood pressure control assessed by home, ambulatory and conventional blood pressure measurements in the Japanese general population: the Ohasama study.

To assess blood pressure control in the Japanese population, we analyzed previously obtained measurements of conventional, home and ambulatory blood pressures in 1,174 subjects aged > or =40 in a Japanese community. On the basis of conventional blood pressure values and the use of antihypertensive medication, participants were classified as normotensive, untreated hypertensive and treated hypertensive subjects. When 140/90, 135/85 and 135/85 mmHg were used as the hypertension criteria for conventional, home and ambulatory blood pressure measurements, respectively, all three blood pressure values were higher in untreated and treated hypertensive subjects than in normotensive subjects. Among the treated hypertensive subjects, approximately half were classified as hypertensive not only by conventional blood pressure, but also by home or ambulatory measurements. Approximately 10% of the subjects defined as normotensive by conventional blood pressure measurement were classified as hypertensive by home or ambulatory measurements, whereas 60% of the untreated hypertensive subjects as defined by conventional blood pressure measurement had normal home or ambulatory blood pressure values. Therefore, we concluded that 1) the poor blood pressure control in treated hypertensive subjects was attributable not only to the white coat effect but also to inadequate control of blood pressure; and 2) a certain percentage of subjects were misclassified as hypertensive or normotensive by conventional blood pressure measurement.

Adult↗
PubMed1993

Ambulatory blood pressure: a predictor of left ventricular mass and future blood pressure in subjects predisposed for hypertension.

Twenty-four-hour ambulatory blood pressure (SpaceLab 5200) and a single laboratory blood pressure were measured in a population-derived sample of normotensive men (mean age 36 years) with (n = 13) or without (n = 16) a positive family history of hypertension. The aim was to determine whether ambulatory monitoring was a better predictor than clinical measurements for echocardiographic derived indices of left ventricular mass and for future blood pressure. At the initial examination ambulatory blood pressure could discriminate between the groups, showing significant differences that were not evident from the clinical blood pressure measurement. After 5 years the blood pressure had increased in the group with a family predisposition for hypertension but only one subject had overt hypertension. The correlation between the average day-time blood pressure and the clinical blood pressure at follow-up was only marginally better than the correlation for the initial clinical blood pressure. In contrast to the clinical blood pressure, both day-time and night-time blood pressure averages were significantly correlated to left ventricular mass at the initial examination. It is concluded that in still normotensive subjects, ambulatory monitoring is a better predictor than clinical measurements for left ventricular mass but not for future blood pressure.

Adult↗
PubMed1999

[How reproducible is blood pressure measurement? Intra- and interindividual blood pressure variability in routine practice].

Considering the reproducibility of blood pressure readings the epidemiologist and the physician in his clinical work take two different points of view. Studying drug effects the epidemiologist is interested in significant differences of blood pressures in a study population. The physician however, who estimates the effect of his prescription given to an individual patient has to compare single blood pressure readings in single individuals. In a pharmacological study we accept without any doubt the need of certain numbers of investigations to define a difference of 10 mm Hg as significant. In clinical routine however we behave quite differently and judge single readings intuitively as equal or different, independent of any statistical considerations. Not only the doctor but also the scientific societies with the highest reputation share the same point of view. In their recommendations they accept an arithmetic mean of two blood pressure readings as sufficient to judge blood pressures in individuals. In order to discuss this topic primarily from the doctors point, we analysed repeated blood pressure readings of 21 volunteers who tested 20 different blood pressure devices. We conclude, that the ongoing practice of judging the blood pressures of the patients meets only the needs of the epidemiologist. Reproducibility of single readings or mean values of two readings however are insufficient to draw satisfactory conclusions from the distributions of blood pressure in single individuals. Due to the short and long term blood pressure variability increasing the numbers of readings within a single day does not improve reproducibility sufficiently. It seems that the amount of blood pressure readings which are necessary to improve reproducibility of "the patients blood pressures" should be increased and taken over several days. If this is true, daily self-recordings should be the most promising approach.

Adult↗
PubMed1999

[Reactive increase in blood pressure on immobilization, but not hypertension, prevents pressure ulcers].

Of 135 geriatric patients immobilized for at least 2 days, 37 (27.4%) had pressure ulcers (PU). Those without PU were the control comparison group. Gender, length of immobilization, number of blood pressure determinations and proportion with hypertension were similar in those with and without PU. Those with PU were slightly older than those in the comparison group: 75.5 +/- 8.8 and 74.7 +/- 9.6 years, respectively (p > 0.05). Of 66 patients with acute ischemic stroke, reactive increase of systolic or diastolic blood pressure to 140/90 mm Hg or above following immobilization, was seen in 60.6% and 22.7% of patients, respectively, and there were PU in 12.1%. Of 17 with recurrent ischemic stroke, corresponding figures were: 41.2%, 23.5% (p > 0.05), and 47.1% (p < 0.01). In 7 patients with previous ischemic stroke corresponding figures were: 14.3% and 0% (p < 0.01) and 100% (p < 0.001). In 36 operated for fracture of the femur, corresponding figures were: 50%, 11.1% (p > 0.05), and 27.8% (p > 0.05). For 9 patients with severe infections, sepsis or pneumonia, the corresponding figures were: 22.2% and 0.0% (p > 0.05), and 44.4% (p < 0.04). The proportion of patients with reactive increase in systolic blood pressure on immobilization was lower in the PU group than in the controls, 27% vs 59.2%, (p < 0.001). The corresponding figures for reactive increase in diastolic blood pressure were similar, 8.1% and 20.4%, respectively (p > 0.05). The mean systolic blood pressure on immobilization was higher in the control than in the PU group, 145.4 +/- 21.7 and 130.8 +/- 14.9 mm Hg, respectively (p < 0.001). The corresponding figures for the mean diastolic blood pressure were similar, 81.2 +/- 10.5 and 75.7 +/- 8.9 mm Hg, respectively (p < 0.01). An increase in systolic blood pressure on immobilization reduced the risk of developing PU (p < 0.05). There was no significant statistical relation between diagnosis of hypertension and proportion of patients with PU (p > 0.05). Of 67 patients with hypertension, in 23.9% and 74.6% of them there was no increase in systolic or diastolic blood pressure, respectively. Statistical difference between lack of diastolic or systolic response was very significant (p < 0.001). Reactive increase of blood pressure, but not hypertension, predicts reduced risk of PU on immobilization in the hospitalized elderly. Diminished reactive increase of blood pressure in response to stress of any kind may be a criterion of frailty and reduced physiological reserves. Efforts to reduce elevated blood pressure when a patient is immobilized appear irrational.

Aged↗
PubMed1991

Ambulatory blood pressure monitoring in the assessment of antihypertensive treatment: 24-h blood pressure control with lacidipine once a day.

Ambulatory blood pressure monitoring gives a more representative blood pressure profile than office blood pressure measurements and is free of any placebo effect. It is therefore useful for studying the effect of antihypertensive agents. Although ambulatory blood pressure is less variable than office blood pressure, spontaneous fluctuations have been found in whole-day blood pressure when repeated measurements are taken. In the multicentre Triveneto Study, the mean difference between 24-h blood pressure recordings taken 3 months apart in 85 mild hypertensives was -0.1/-0.7 mmHg and the coefficient of repeatability (2 s.d.) was 17.3/12.6 mmHg. The corresponding values for office blood pressure were -8.7/-2.0 and 29.8/16.5 mmHg, respectively. This reduction in inter-measurement variability with ambulatory blood pressure monitoring makes it possible to reduce the sample size required to prove the effect of an antihypertensive agent in pharmacological trials. However, in the individual subject, the results of ambulatory blood pressure monitoring should be considered with caution, as 24-h blood pressure averages and profiles are subject to a degree of variability. This technique was used in 21 mild-to-moderate hypertensives to test the antihypertensive effect of lacidipine given once a day (4-6 mg) versus placebo. The drug proved effective throughout the day and night, showing a 24-h effect on blood pressure without reflex tachycardia or other intolerable side effects.

Adult↗
PubMed1991

Low frequency arterial wall movements for indirect blood pressure measurement in man. Validation of a method for non-invasive assessment of blood pressure under the influence of isoprenaline and angiotensin.

In order to measure blood pressure noninvasively, the second derivative of the low frequency wall movements of the brachial artery were registered with a piezo-electric pressure probe during deflation of a Riva-Rocci cuff along with the actual cuff pressure. Two characteristic phenomena of this signal have been suggested to reflect systolic and diastolic blood pressure. Appearance of a positive spike phenomenon (S) was suggested to indicate systolic blood pressure and disappearance of a negative preanacrotic notch (D) to indicate diastolic blood pressure. To prove the validity of these suggestions, these phenomena were assessed in 10 young healthy males during isoprenaline and angiotensin induced changes of blood pressure. Intraarterial (A. radialis) and auscultatory (A. brachialis) blood pressures were recorded simultaneously. Determination of systolic blood pressure with the S phenomenon agreed well with invasive and auscultatory results. Invasive diastolic values agreed well with the cuff pressure at the last signal before disappearance of the preanacrotic notch (D1). Data from auscultation agreed less well with the D1 phenomenon. With increasing doses of isoprenaline, the diastolic measurements (D1) tended to be lower than the invasive ones. However, this discrepancy was far discreeter than that seen with ordinary auscultatory blood pressure measurement. We therefore conclude that registrations of low frequency arterial wall movements yield distinct characteristic spike phenomena useful for measurement of blood pressure in good agreement with the invasive method. In addition, the method provides clearly documented records and should be useful in situations which rely on a valid indirect method.

Adult↗
PubMed1990

[Correlation of arterial pressure in the forearm with blood pressure in the ascending aorta].

Forearm blood pressures obtained by auscultation were compared with the data of pressure recording in the ascending aorta during diagnostic catheterization in 243 patients with coronary heart disease, arterial hypertension and some malformations of the heart. With indirect measurement, systolic blood pressure was shown to be sufficiently reliable and to characterize systolic pressure in the ascending aorta with assurance, the pressure in the aorta being slightly less (some 10%) in approximately half the cases. The regression equation for systolic pressure in the ascending aorta against forearm pressure is as follows: Y = 0.96X - 1. Measurement of diastolic pressure in the ascending aorta yields less accuracy, so it is advisable to use two regression equations: (1) Y = 0.98X - 1 for a diastolic pressure of 80 mm Hg or less and (2) Y = 0.85X + 2 for a pressure of greater than 80 mm Hg. Thus, ascending aorta pressure values required for invasive hemodynamic studies may be satisfactorily calculated from the data of blood pressure auscultative measurement.

Aorta↗
PubMed1989

[Experimental study on the changes in circulatory kinetics due to an increase of intraabdominal pressure: the effective monitoring of the pressure of inferior vena cava].

We examined the change in circulatory kinetics due to an increase in intraabdominal pressure by adding pressure quantitatively to the abdominal wall by means of the manchette technique by using mongrel dogs, and obtained the following results: 1) By adding to the pressure to the abdominal wall, the pressure of inferior vena cava at the confluence of right and left common iliac veins showed a significantly higher value (p less than 0.05) than those at other 4 areas of the vena cava from just above the diaphragm to the above confluence. 2) All the dogs in the group with 20mmHg pressure survived for 24 hours, while those in the group with 40mmHg pressure died in all after survival between 13.8 +/- 2.05 hours. 3) The pressures of the inferior vena cava at the confluence of right and left common iliac veins with 20 and 40mmHg showed no significant difference immediately after the pressurization, but thereafter showed a increasing tendency in the group with 40mmHg (p less than 0.05). This increase in the pressure of the inferior vena cava lead to peripheral circulatory insufficiency. 4) The measurement of the pressure of the inferior vena cava at the confluence of right and left iliac veins in case of increased intraabdominal pressure seems to be an effective index for the risk of intraabdominal pressure.

Abdomen↗
PubMed1996

Left ventricular intramyocardial pressure determination using two different solid-state micromanometric pressure sensors.

Intramyocardial tissue pressure can influence distribution of ventricular blood flow and dynamics during the cardiac cycle. Left ventricular ventral wall subepicardial and subendocardial tissue pressures were measured simultaneously using two different types of solid-state micromanometers (5F Millar model SPR-230 and Konigsberg Instruments model P19 pressure transducers) and compared with left ventricular cavity pressure. Systolic pressures recorded by Millar and Konigsberg transducers were similar when the sensor surfaces faced the left ventricular cavity either in the endocardium or epicardium. Diastolic pressures in the epicardium were higher than left ventricular cavity pressure. When Millar and Konigsberg transducer were placed in the epicardium, with the pressure sensors facing epicardially, the output signal of the Millar transducer was out of phase with the signal of the Konigsberg transducer and left ventricular chamber pressure outputs. Results indicate that output signals for intramyocardial pressures vary depending on the direction of the Millar or Konigsberg pressure sensor in the left ventricular wall. Thus, pressure output signals vary depending on configuration of the sensor surface, relative flexibility of the connecting cables, and orientation of the sensor surface with respect to left ventricular anatomy.

Diastole↗
PubMed1996

The effect of positive pressure breathing for altitude protection on intraocular pressure.

BACKGROUND: The effect of positive pressure breathing for altitude protection (PBA) on intraocular pressure was studied; the behavior of intraocular pressure both during and after PBA exposure was of particular interest. METHODS: Seven subjects were exposed to PBA of up to 60 mmHg at ground-level. The subjects were seated, and wore an aircrew helmet (HGU-55/P), oro-facial mask (M8U-20/P), thoracic counterpressure garment (CSU-17/P) and an extended coverage G-suit (ATAGS). Before, during and after each exposure, intraocular pressure was measured using a Tono-Pen XL applanation tonometer. RESULTS: All 7 subjects completed 10 min of PBA at breathing pressures of 30 and 40 mmHg, and 6 subjects completed 10 min at 50 and 60 mmHg. Mean and SEM increases in intraocular pressure, as compared to pre-exposure baseline measurements, were 7.7 +/- 0.6 mmHg at a breathing pressure of 30 mmHg, 12.0 +/- 0.9 mmHg at 40 mmHg, 18.4 +/- 1.3 mmHg at 50 mmHg and 20.0 +/- 0.6 mmHg at 60 mmHg. The difference between each of these increases was significant (p < 0.05), with the exception of that between 50 and 60 mmHg PBA. CONCLUSIONS: Intraocular pressure increases as breathing pressure increases. It is likely that this change in intraocular pressure would provide some protection to the retinal vasculature during PBA. In addition, it is unlikely that the temporary elevation of intraocular pressure following pressure breathing is of medical concern.

Adult↗