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Biomedical subjects

John F Potter

Publications and source records attributed to John F Potter.

At least 19 recordsLinked to original sources
PubMed2006

Pressor therapy in acute ischemic stroke: systematic review.

BACKGROUND AND PURPOSE: Systolic blood pressure (SBP) levels below 140 mm Hg after acute stroke occur in 18% to 25% of patients, and may be associated with adverse outcome, in terms of death and disability. It has thus been proposed that BP elevation in acute ischemic stroke may be beneficial by increasing perfusion to the peri-infarct penumbra, though not only in those with low BP levels. METHODS: All articles studying BP elevation in the context of acute stroke were identified using a structured search strategy. RESULTS: Two reviewers independently searched the databases, and 12 relevant publications were identified. All identified publications related to acute ischemic stroke and no articles on pressor therapy in primary hemorrhagic stroke were found. The review included 319 subjects (age: 42 to 88 years, 46% male), with phenylephrine being the most commonly used pressor agent, though 8 studies incorporated volume expansion. Because of small numbers, and varying entry/outcome criteria, no meta-analysis of outcome measures was possible. Overall, in these few studies undertaken, pressor therapy in acute stroke appears feasible and well-tolerated. The benefit and risks in terms of clinical outcomes remains unknown, but intensive monitoring is advised if such therapy is undertaken. CONCLUSIONS: Theoretical arguments exist for inducing BP elevation in acute ischemic stroke to increase blood flow to the ischemic penumbra across patients with a broad BP range. To date, there have only been a few small trials with inconclusive results. Many questions are still unanswered about the safety and potential benefits of pressor therapy in acute stroke. Hopefully, ongoing trials will answer some of these important questions.

Blood Pressure↗
PubMed2006

Multiple coherence of cerebral blood flow velocity in humans.

The coherence function has been used in transfer function analysis of dynamic cerebral autoregulation to assess the statistical significance of spectral estimates of gain and phase frequency response. Interpretation of the coherence function and choice of confidence limits has not taken into account the intrinsic nonlinearity represented by changes in cerebrovascular resistance due to vasomotor activity. For small spontaneous changes in arterial blood pressure (ABP), the relationship between ABP and cerebral blood flow velocity (CBFV) can be linearized, showing that corresponding changes in cerebrovascular resistance should be included as a second input variable. In this case, the standard univariate coherence function needs to be replaced by the multiple coherence, which takes into account the contribution of both inputs to explain CBFV variability. With the use of two different indicators of cerebrovascular resistance index [CVRI = ABP/CBFV and the resistance-area product (RAP)], multiple coherences were calculated for 42 healthy control subjects, aged 20 to 40 yr (28 +/- 4.6 yr, mean +/- SD), at rest in the supine position. CBFV was measured in both middle cerebral arteries, and ABP was recorded noninvasively by finger photoplethysmography. Results for the ABP + RAP inputs show that the multiple coherence of CBFV for frequencies <0.05 Hz is significantly higher than the corresponding values obtained for univariate coherence (P < 10(-5)). Corresponding results for the ABP + CVRI inputs confirm the principle of multiple coherence but are less useful due to the interdependence between CVRI, ABP, and CBFV. The main conclusion is that values of univariate coherence between ABP and CBFV should not be used to reject spectral estimates of gain and phase, derived from small fluctuations in ABP, because the true explained power of CBFV in healthy subjects is much higher than what has been usually predicted by the univariate coherence functions.

Adult↗
PubMed2005

Cerebral blood flow velocity during mental activation: interpretation with different models of the passive pressure-velocity relationship.

The passive relationship between arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) has been expressed by a single parameter [cerebrovascular resistance (CVR)] or, alternatively, by a two-parameter model, comprising a resistance element [resistance-area product (RAP)] and a critical closing pressure (CrCP). We tested the hypothesis that the RAP+CrCP model can provide a more consistent interpretation to CBFV responses induced by mental activation tasks than the CVR model. Continuous recordings of CBFV [bilateral, middle cerebral artery (MCA)], ABP, ECG, and end-tidal CO(2) (EtCO(2)) were performed in 13 right-handed healthy subjects (aged 21-43 yr), in the seated position, at rest and during 10 repeated presentations of a word generation and a constructional puzzle paradigm that are known to induce differential cortical activation. Due to its small relative change, the CBFV response can be broken down into standardized subcomponents describing the relative contributions of ABP, CVR, RAP, and CrCP. At rest and during activation, the RAP+CrCP model suggested that RAP might reflect myogenic activity in response to the ABP transient, whereas CrCP was more indicative of metabolic control. These different influences were not reflected by the CVR model, which indicated a predominantly metabolic response. Repeated-measures multi-way ANOVA showed that CrCP (P = 0.025), RAP (P = 0.046), and CVR (P = 0.002) changed significantly during activation. CrCP also had a significant effect of paradigm (P = 0.045) but not hemispheric dominance. Both RAP (P = 0.039) and CVR (P = 0.0008) had significant effects of hemispheric dominance but were not sensitive to the different paradigms. Subcomponent analysis can help with the interpretation of CBFV responses to mental activation, which were found to be dependent on the underlying model of the passive ABP-CBFV relationship.

Adult↗
PubMed2005

Dynamic cerebral autoregulation during brain activation paradigms.

Dynamic cerebral autoregulation (CA) describes the transient response of cerebral blood flow (CBF) to rapid changes in arterial blood pressure (ABP). We tested the hypothesis that the efficiency of dynamic CA is increased by brain activation paradigms designed to induce hemispheric lateralization. CBF velocity [CBFV; bilateral, middle cerebral artery (MCA)], ABP, ECG, and end-tidal Pco(2) were continuously recorded in 14 right-handed healthy subjects (21-43 yr of age), in the seated position, at rest and during 10 repeated presentations (30 s on-off) of a word generation test and a constructional puzzle. Nonstationarities were not found during rest or activation. Transfer function analysis of the ABP-CBFV (i.e., input-output) relation was performed for the 10 separate 51.2-s segments of data during activation and compared with baseline data. During activation, the coherence function below 0.05 Hz was significantly increased for the right MCA recordings for the puzzle tasks compared with baseline values (0.36 +/- 0.16 vs. 0.26 +/- 0.13, P < 0.05) and for the left MCA recordings for the word paradigm (0.48 +/- 0.23 vs. 0.29 +/- 0.16, P < 0.05). In the same frequency range, significant increases in gain were observed during the puzzle paradigm for the right (0.69 +/- 0.37 vs. 0.46 +/- 0.32 cm.s(-1).mmHg(-1), P < 0.05) and left (0.61 +/- 0.29 vs. 0.45 +/- 0.24 cm.s(-1).mmHg(-1), P < 0.05) hemispheres and during the word tasks for the left hemisphere (0.66 +/- 0.31 vs. 0.39 +/- 0.15 cm.s(-1).mmHg(-1), P < 0.01). Significant reductions in phase were observed during activation with the puzzle task for the right (-0.04 +/- 1.01 vs. 0.80 +/- 0.86 rad, P < 0.01) and left (0.11 +/- 0.81 vs. 0.57 +/- 0.51 rad, P < 0.05) hemispheres and with the word paradigm for the right hemisphere (0.05 +/- 0.87 vs. 0.64 +/- 0.59 rad, P < 0.05). Brain activation also led to changes in the temporal pattern of the CBFV step response. We conclude that transfer function analysis suggests important changes in dynamic CA during mental activation tasks.

Adult↗
PubMed2005

Bendrofluazide fails to reduce elevated blood pressure levels in the immediate post-stroke period.

INTRODUCTION: Blood pressure (BP) levels, beat-to-beat blood pressure variability, dynamic cerebral autoregulation and cardiac baroreceptor sensitivity are frequently abnormal following acute stroke and are associated with an adverse short- and long-term prognosis. Thiazide diuretics are effective antihypertensive agents in preventing primary and secondary stroke, but their hypotensive and cerebral autoregulatory effects in the immediate post-stroke period have not been studied. METHODS: Thirty-seven hypertensive neuroradiologically proven ischaemic stroke patients were randomized in a double-blind, placebo controlled, parallel group study to bendrofluazide 2.5 mg daily or matching placebo, within 96 h of stroke onset, for a 7-day period. Casual and non-invasive beat-to-beat arterial BP levels, cerebral blood flow velocity, ECG and transcutaneous carbon dioxide levels were measured within 70 +/- 20 h of cerebral infarction and again 7 days later. Dynamic cerebral autoregulatory indices, pulse interval, BP variability and cardiac baroreceptor sensitivity were also calculated. RESULTS: Small, non-significant falls were seen in casual and beat-to-beat BP levels over the 7-day period in both active and placebo-treated patients with no differences between treatments. No significant changes were seen in dynamic cerebral autoregulation or in cardiac baroreceptor sensitivity during the follow-up in either group. CONCLUSION: Following acute ischaemic stroke, the standard dose of bendrofluazide at 2.5 mg daily in this study sample did not lower systemic BP levels over the subsequent 7-day period. There was no evidence that bendrofluazide significantly altered cerebral autoregulation or improved cardiac baroreceptor sensitivity post-ictus. Bendrofluazide appears to be an ineffective hypotensive agent at the standard dosage in the initial post-stroke period.

Aged↗
PubMed2005

Cerebral and systemic hemodynamic changes during cognitive and motor activation paradigms.

Cognitive and/or sensorimotor stimulations of the brain induce increases in cerebral blood flow that are usually associated with increased metabolic demand. We tested the hypothesis that changes in arterial blood pressure (ABP) and arterial Pco(2) also take place during brain activation protocols designed to induce hemispheric lateralization, leading to a pressure-autoregulatory response in addition to the metabolic-driven changes usually assumed by brain stimulation paradigms. Continuous recordings of cerebral blood flow velocity [CBFV; bilateral, middle cerebral artery (MCA)], ABP, ECG, and end-tidal Pco(2) (Pet(CO(2))) were performed in 15 right-handed healthy subjects (aged 21-43 yr), in the seated position, at rest and during 10 repeated presentations of a word generation and a constructional puzzle paradigm that are known to induce differential cortical activation. Derived variables included heart rate, cerebrovascular resistance, critical closing pressure, resistance area product, and the difference between the right and left MCA recordings (CBFV(R-L)). No adaptation of the CBFV(R-L) difference was detected for the repeated presentation of 10 activation tasks, for either paradigm. During activation with the word generation tasks, CBFV changed by (mean +/- SD) 9.0 +/- 3.7% (right MCA, P = 0.0007) and by 12.3 +/- 7.6% (left MCA, P = 0.0007), ABP by 7.7 +/- 6.0 mmHg (P = 0.0007), heart rate by 7.1 +/- 5.3 beats/min (P = 0.0008), and Pet(CO(2)) by -2.32 +/- 2.23 Torr (P = 0.002). For the puzzle paradigm, CBFV changed by 13.9 +/- 6.6% (right MCA, P = 0.0007) and by 11.5 +/- 6.2% (left MCA, P = 0.0007), ABP by 7.1 +/- 8.4 mmHg (P = 0.0054), heart rate by 7.9 +/- 4.6 beats/min (P = 0.0008), and Pet(CO(2)) by -2.42 +/- 2.59 Torr (P = 0.001). The word paradigm led to greater left hemispheric dominance than the right hemispheric dominance observed with the puzzle paradigm (P = 0.004). We concluded that significant changes in ABP and Pet(CO(2)) levels occur during brain activation protocols, and these contribute to the evoked change in CBFV. A pressure-autoregulatory response can be observed in addition to the hemodynamic changes induced by increases in metabolic demand. Simultaneous changes in Pco(2) and heart rate add to the complexity of the response, indicating the need for more detailed modeling and better understanding of brain activation paradigms.

Adult↗
PubMed2005

Abnormalities in cardiac baroreceptor sensitivity in acute ischaemic stroke patients are related to aortic stiffness.

Cardiac BRS (baroreceptor reflex sensitivity) is impaired following ischaemic stroke and predicts the risk of subsequent long-term death and disability. Impaired cardiac BRS may be due to impaired central processing of baroreceptor information following stroke or reduced baroreceptor activity due to increased large artery stiffness. We evaluated the relationship between large (aortic) artery stiffness and cardiac BRS during the acute phase of ischaemic stroke and in comparison with a group of stroke-free control subjects. Thirty-one ischaemic stroke patients were studied within 48 h of onset and again on day 14, along with 26 control subjects free of cerebrovascular disease. Cardiac BRS (determined by spectral analyses) and arterial stiffness estimated by PWVcf (carotid-femoral pulse wave velocity) using applanation tonometry were obtained. At baseline, cardiac BRS was lower in the stroke compared with the control group (4.3+/-2.3 compared with 6.5+/-4.2 ms/mmHg; P < 0.05). Cardiac BRS values were correlated with PWVcf at < 48 h (r = -0.51, P < 0.01) and on day 14 (r = -0.54, P < 0.01), but not in the control group (r = -0.27, P = not significant). In quantile regression models, taking into account the effect of all cardiovascular variables, cardiac BRS was independently related to PWVcf at baseline and on day 14 in the stroke patients, but stroke was not related to cardiac BRS level when other cardiovascular variables were considered. Wall stiffness of the arterial vessels involved in the baroreflex arc may account for, at least in part, the reduced cardiac BRS observed in acute stroke patients.

Acute Disease↗
PubMed2005

Assessment of cerebral autoregulation from ectopic heartbeats.

Transfer function analysis of spontaneous fluctuations in BP (blood pressure) and CBFV (cerebral blood flow velocity) has been widely used to study dynamic CA (cerebral autoregulation). The inverse Fourier transform and its integral, giving the impulse and step responses, have been used to gain perspective of the state of dynamic CA from the frequency and time domains respectively. The occurrence of ectopic heartbeats in the data has usually been treated as an artefact. Data containing multiple ectopic heartbeats were selected from a data set compiled for an acute stroke study which also included bilateral middle CBFV, concurrent surface ECG and non-invasive beat-to-beat BP recordings. Transfer function analysis and impulse and step responses were calculated from these data by (i) retaining ectopic heartbeats, (ii) after removal of ectopic heartbeats and replacement by linear interpolation, and (iii) using a narrow window of data surrounding selected ectopic heartbeats. Coherent averaging of the raw data of the selected ectopic heartbeats also allowed direct visualization of the relationship between BP changes and CBFV. The impulse and step responses were similar in shape whether or not ectopic heartbeats had been removed and showed characteristics of active dynamic CA. Removal of ectopic heartbeats from the CBFV and BP tracings, by linear interpolation or other methods, is not necessary to provide reliable estimates of dynamic autoregulation in subjects with ectopic heartbeat rates of up to eight per min. Additionally, impulse-like disturbances of BP induced by single-beat ectopic heartbeats provide enough information to characterize the autoregulatory response of the subject in agreement with more traditional methods of dynamic autoregulation assessment.

Aged↗
PubMed2004

Influence of controlled breathing patterns on cerebrovascular autoregulation and cardiac baroreceptor sensitivity.

Transfer function analysis has become one of the main techniques to study the dynamic relationship between cerebral blood flow and arterial blood pressure, but the influence of different respiratory rates on cerebral blood flow has not been fully investigated. In 14 healthy volunteers, middle cerebral artery blood flow velocity, recorded using transcranial Doppler ultrasound, non-invasive beat-to-beat Finapres blood pressure, ECG and end-tidal CO(2) ( P ECTO(2)) levels were recorded with subjects resting supine and breathing spontaneously or at controlled rates of 6, 10 and 15 breaths/min. Transfer function analysis and impulse and step responses were computed at each respiratory rate. P ECTO(2) levels tended to fall slightly during paced respiration, especially at 15 breaths/min. Controlled breathing rates did not alter transfer function analysis in the frequency range below 0.08 Hz but, above this frequency, the coherence function contained significant peaks corresponding to the respiratory frequencies. The impulse response was similar at all breathing rates, but the step response was characteristic of more efficient autoregulation with reduced P ECTO(2) levels associated with increasing respiratory rate. The effects of breathing rate and rhythmicity and P ECTO(2) must be considered in studies of cerebral autoregulation.

Adult↗
PubMed2004

Blood pressure in acute stroke.

Elevated systolic blood pressure levels (> or =160 mmHg) are a common complication of acute stroke, affecting up to 60% of patients, and providing an immediate management dilemma in the 40% of acute stroke patients on pre-existing antihypertensive therapy. There are theoretical reasons for both lowering blood pressure in the acute stroke situation, as well as leaving raised levels untreated. Furthermore, low systolic blood pressure levels (< or =140 mmHg), though a less common problem affecting approximately 20% of patients, may also be associated with increased morbidity and mortality. However, limited data exists from randomised, placebo-controlled trials to inform as to the optimum management of acute stroke blood pressure. This review will consider the evidence for and against the therapeutic manipulation of acute stroke blood pressure, and discuss the information currently available from observational and therapeutic intervention trials, as well as consider the ongoing clinical trials in this area.

Acute Disease↗
PubMed2004

The systemic haemodynamic and cerebral autoregulatory effects of bendrofluazide in the subacute post-stroke period.

INTRODUCTION: Little data exist on the efficacy in terms of blood pressure reduction or outcome measures for the various antihypertensive agents in patients post-stroke. In this study the effects of bendrofluazide on blood pressure levels and variability, dynamic cerebral autoregulation and cardiac baroreceptor sensitivity were assessed in the sub-acute stroke period. METHODS: A total of 36 hypertensive ischaemic stroke patients were randomized to oral bendrofluazide 2.5 mg daily or matching placebo starting 10 days post-ictus and continued for 28 days. A total of 12 hypertensive controls were similarly randomized in a double-blind, crossover study, each limb being of 28 days duration. Cerebral blood flow velocity, non-invasive beat-to-beat blood pressure levels, electrocardiograms (ECGs) and transcutaneous carbon dioxide levels were measured before and at the end of each treatment period in stroke and control subjects. RESULTS: Casual blood pressure levels were not significantly reduced in stroke patients with bendrofluazide, but in the placebo group levels increased by 13 +/- 13/6 +/- 7 mmHg (P < 0.001) at study termination. In the control group, casual systolic blood pressure fell during active treatment by 12 +/- 16 mmHg (P < 0.03) compared with placebo. Dynamic cerebral autoregulation, beat-to-beat blood pressure variability and cardiac baroreceptor sensitivity did not change with bendrofluazide or placebo in either the stroke patients or controls. CONCLUSION: Bendrofluazide does not appear to be an effective hypotensive agent in the sub-acute post-stroke period but may limit the blood pressure rise seen during stroke recovery. Bendrofluazide however does not adversely influence dynamic cerebral autoregulation, blood pressure variability or cardiac baroreceptor sensitivity in either strokes or control subjects.

Adult↗
PubMed2003

Effect of aging on dynamic cerebral autoregulation during head-up tilt.

BACKGROUND AND PURPOSE: Physiological aging is associated with many changes in the cardiovascular and cerebrovascular systems, but dynamic cerebral autoregulation (CA) during supine rest shows no age-related changes. Because syncopal syndromes usually occur during orthostatic stress and their prevalence increases with age, it is important to define the effect of aging on dynamic CA during orthostatic stress. METHODS: Twenty-five younger subjects (</=40 years) and 25 sex-matched older subjects (>/=60 years) underwent 70 degrees head-up tilt for 30 minutes. Bilateral middle cerebral artery blood flow velocities were measured with transcranial Doppler ultrasound, along with noninvasive continuous measurements of arterial blood pressure, heart rate, and transcutaneous and end-tidal carbon dioxide concentrations. By comparing actual changes in cerebral blood flow velocity to changes predicted by a model based on arterial blood pressure changes, we derived dynamic autoregulatory indexes for each subject for periods before, during, and after tilt. RESULTS: Younger subjects were a mean of 40 years younger than older subjects (28+/-8 versus 69+/-10 years). Although cerebral blood flow velocity (P<0.001) and baroreceptor sensitivity (P<0.001) were significantly lower at rest in older subjects, autoregulatory indexes were similar in younger and older subjects at all times before, during, and after tilt (P=0.62). CONCLUSIONS: Although increasing age is associated with lower cardiac baroreceptor sensitivity and cerebral blood flow velocity, dynamic CA during orthostatic stress is unaffected by physiological aging.

Adolescent↗
PubMed2003

Cardiac baroreceptor sensitivity predicts long-term outcome after acute ischemic stroke.

BACKGROUND AND PURPOSE: The baroreceptor reflex arc is important in the short-term regulation of the cardiovascular system, and small studies have reported impaired cardiac baroreceptor sensitivity (BRS) after acute stroke. However, the prognostic significance of impaired BRS is uncertain. METHODS: One hundred twenty-four patients underwent simultaneous ECG and noninvasive beat-to-beat blood pressure (BP) monitoring within 72 hours of neuroradiologically confirmed acute ischemic stroke. Cardiac BRS was assessed from the combined alpha-index by means of power spectral analysis techniques. Baseline data for acute stroke patients were compared with those of a control group matched for age, sex, and casual BP. Patients were followed up for a median of 1508 days (range, 9 to 2656 days), and outcome was compared between patients with and without impaired BRS. RESULTS: Median BRS values were significantly lower in stroke patients than in controls (5 [interquartile range, 3.5 to 7.4] versus 6.2 [interquartile range, 4.5 to 8.3] ms/mm Hg; P=0.04). Sixty-one (33 male) patients (mean age, 70.2 [SD 10.5] years) had impaired BRS (< or =5.0 ms/mm Hg) compared with 63 (35 male) patients (mean age, 70.6 [SD 11.7] years) without impaired BRS (>5.0 ms/mm Hg). Stroke patients with impaired BRS values had a significantly poorer prognosis (28% versus 8% mortality rate during the follow-up period) although there were no differences in age, stroke severity, stroke type, or casual or 24-hour BP parameters between the 2 groups. CONCLUSIONS: Impaired cardiac BRS is associated with increased long-term mortality after acute ischemic stroke, irrespective of age, sex, stroke type, and BP. This may reflect cardiac arrhythmias, but the mechanisms underlying this association are unknown, although therapies that improve cardiac BRS after stroke warrant further investigation.

Acute Disease↗
PubMed2003

Short-term variability of cerebral blood flow velocity responses to arterial blood pressure transients.

The time course of mean beat-to-beat changes in cerebral blood flow velocity changes induced by spontaneous transients in mean arterial blood pressure was studied in a group of 39 healthy subjects, ages 40 +/- 15 (SD) years. Continuous 10-min noninvasive recordings of cerebral blood flow velocity (CBFV) from both middle cerebral arteries (MCA) with Doppler ultrasound (US) and simultaneous beat-to-beat arterial blood pressure (ABP) were made. A total of 522 spontaneous positive transients of ABP and CBFV were extracted with a maximum of 15 transients for each subject. The CBFV transient amplitude was normalized by the corresponding ABP change and the area-under-the-curve (AUC) of the falling phase was used to classify the CBFV regulatory response as either weak, moderate or strong. The coherent average of ABP and CBFV of each category confirmed the consistency of this classification, reinforced by the agreement of separate averages for recordings from the right and left MCA. All 39 subjects showed at least two categories of transients, with all three categories present in 33 subjects (right MCA) and 29 subjects (left MCA), respectively. These results indicate a significant short-term variability of CBFV responses in healthy subjects whose origin remains unexplained.

Adult↗
PubMed2003

Cerebral autoregulation indices are unimpaired by hypertension in middle aged and older people.

BACKGROUND: Hypertension is known to increase the limits of static cerebral autoregulation (CA) but its effects on other aspects of CA such as efficiency and latency are unknown. In this study we test the hypothesis that dynamic cerebral autoregulation and the efficiency of static cerebral autoregulation are impaired by untreated hypertension. METHODS: Cerebral blood flow velocity was recorded using transcranial Doppler ultrasound, along with noninvasive beat-to-beat blood pressure (BP), electrocardiogram, and transcutaneous carbon dioxide levels, with subjects at rest and during isometric hand grip, thigh cuff, and the Valsalva maneuver. Static and dynamic CA indices were calculated. RESULTS: No significant difference was seen in static or dynamic CA indices between normotensive and hypertensive groups for any pressor or depressor stimulus. Spearman's rank correlation showed no relation between static or dynamic CA indices and systemic BP levels for all maneuvers, but a significant relationship between age and static CA index, determined using isometric handgrip (P =.002), was found. CONCLUSIONS: In middle-aged and older people, sustained untreated hypertension does not alter dynamic CA or the efficiency of static CA within the BP limits studied.

Age Factors↗
PubMed2003

Cardiovascular effects of acute oxygen administration in healthy adults.

Supplementary oxygen is commonly administered in current medical practice. However, attention has recently been drawn to the potentially disadvantageous hemodynamic consequences in certain patients. Possible mechanisms underlying the cardiovascular responses to acute hyperoxia are unclear. The effects of acute oxygen administration on heart rate, blood pressure, cardiac output, systemic vascular resistance, and baroreflex sensitivity were studied in a series of randomised, placebo-controlled studies in healthy individuals, using validated, non-invasive techniques. The effects of oxygen administration on forearm blood flow responses to locally administered acetylcholine, an endothelium-dependent vasodilator, sodium nitroprusside, an endothelium-independent vasodilator, and l-NG-monomethylarginine, a nitric oxide synthase inhibitor, were studied using venous occlusion plethysmography. Oxygen administration for 1 hour caused a reduction in heart rate (P < 0.01) and cardiac index (P < 0.05), and an increase in mean arterial pressure (P < 0.01), systemic vascular resistance (P < 0.05), large artery stiffness (P < 0.05), and baroreflex sensitivity (P < 0.05). There were no effects on vascular responses in the isolated forearm bed. These findings indicate that oxygen administration causes acute effects on cardiovascular function, which might be important in the context of acute illness.

Acetylcholine↗