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Query: UMLS:C0038454 (stroke)
 147,016 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study was undertaken to ascertain the suitability of impedance cardiography for qualifying cardiac output during water immersion where the electrodes were wet. The cardiac output was compared during wet and dry immersion with the head above water by breath holding briefly at 3 lung volumes. For dry immersion, the subjects were protected from contacting water during immersion by enveloping the whole body in a thin plastic bag. For wet immersion, the subject went into the water wearing only trunks. Eleven healthy males served as subjects. Both basal thoracic impedance and the minimum rate of impedance change decreased during wet immersion. These changes were specific, which insignificantly influenced the computation of stroke volume as compared to dry immersion. Our results showed no statistical differences between wet and dry immersions, and between measurements made at total lung capacity functional residual capacity, or residual volume. It is concluded that impedance cardiography is applicable directly in wet conditions without having to protect the subject from getting wet.
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PMID:Cardiac output by impedance cardiography during head-out water immersion. 372 86

The well-known negative correlation between initial value and difference score, referred to as the law of initial value (LIV), is analyzed in the present study. It is shown that whenever the correlation between the initial and final values is less than 1.00, the negative correlation is influenced by the a(a - b) effect. By relating values to the first principal component axis, this spurious effect can be eliminated, thus allowing analysis of any real dependency on initial values. Data collected in a psychophysiological experiment were used to test this hypothesis. A subject sample of 125 male students experienced various challenges (Cold Pressor Test, breath holding, reaction time measurement, digit-series test) while several physiological variables (e.g. blood pressure, stroke volume, electrodermal activity) were monitored. Results fail to support the LIV as originally advanced by Wilder. On the contrary, after eliminating the a(a - b) effect, a positive dependency as indicated by the slope of the first principal component axis (anti-LIV) was observed. The reciprocal relationship between the LIV and anti-LIV is discussed with respect to the measures employed. Advantages and disadvantages of various methods to correct for the initial value dependency are presented.
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PMID:The law of initial value: a rare exception. 375 85

In 12 patients with systemic hypertension the cardiac stroke volume was determined simultaneously by the dye dilution technique and by impedence cardiography. The impedance stroke volume was calculated using Kubicek's formula (using four different values of blood resistivity) and also by the formula sv=AL delta z/Z0 (from the transthoracic impedance change, the delta z waveform). Significant correlations were found between the stroke volume measured by the impedance and reference methods and there were significant differences between the correlation coefficients (range 0.81-0.92) irrespective of which formula was used or which value of blood resistivity was inserted in the Kubicek formula. Only the delta z formula gave no significant differences for both the mean difference and the regression coefficient. Measurement of the stroke volume with the delta z formula requires breath holding, but determination of the systolic ejection time or blood resistivity is not necessary, unlike the Kubicek formula. A low peak value of dz/dt indicated a poor correlation with the dye dilution method, and also indicated a reduced maximum rate of ejection of blood from the heart. The effective delta z formula affords a different approach for future investigations of the genesis of the cardiac impedance changes in the thorax.
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PMID:Stroke volume measurement by impedance cardiography using a formula based on the delta z waveform. 612 90

In nine anesthetized and ventilated dogs heart block was induced at thoracotomy, a pacemaker was inserted, and an electromagnetic flow transducer was placed round the main pulmonary artery. The chest was then closed. Stroke volume (SV) was varied by changing central blood volume. Ventilatory dead space (VDS) and alveolar nitrogen mixing efficiency (ANME) were measured at three levels of heart rate (HR) and three levels of SV independently varied during life and also after cessation of heartbeat. Neither VDS nor ANME showed a significant change with HR or SV during life, but mean VDS increased by 43 ml (22%) and mean ANME decreased by 4.4% postmortem. We conclude that cardiac action increases gas mixing at the interface between inspired and resident gas but has only a small effect on gas mixing distal to the interface during respiration without breath holding.
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PMID:Effect of heart rate and stroke volume on gas mixing in dog lung. 715 56

Impedance cardiography is a reliable method for estimating stroke volume (SV). Breathing, however, causes artefacts, which can be avoided by measuring during breath holding. This study investigated whether SV determination is accurate during breath holding. Twelve healthy subjects were tested in the supine position at rest and during two levels of exercise: 100 and 200 W. Averaged SV values were monitored by means of impedance cardiography before and after endexpiratory breath holding. During breath holding, SV measurement was on a beat-to-beat basis. An obvious decrease in SV during breath holding was noticed, being significant only during exercise (mean decrease of 38% at 100 W and 58% at 200 W). The rest measurements were repeated with open and closed glottis, which yielded the same results. This indicates that the SV decrease was not caused by a Valsalva-like manoeuvre. The mean SV value calculated by means of impedance cardiography for the total breath hold period was significantly lower than the SV during breathing, both at rest (91.7 +/- 2.4%) and at 100 W (90.5 +/- 7.0%). From this study it can be concluded that averaging of the impedance signal, measured while the subject is breathing, is preferential to measuring during breath holding, because the latter condition systematically underestimates SV.
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PMID:The lowering of stroke volume measured by means of impedance cardiography during endexpiratory breath holding. 874 74

Several studies have demonstrated a clear association between snoring, sleep apnoea and increased risk of stroke. However, the possible role of sleep apnoea in the pathophysiogenetic mechanisms of cerebrovascular disease is still unknown. Our aim in this study was to investigate cerebral haemodynamic changes during the waking state in eight patients with sleep apnoea syndrome (OSAS) by means of transcranial Doppler (TCD). In particular, we studied cerebral vascular reactivity (CVR) to hypercapnia calculated by means of the breath holding index (BHI). The investigation was performed in the early morning, soon after awakening, and in the late afternoon. Data were compared with those of eight healthy subjects matched for age and vascular risk factors. OSAS patients showed significantly lower BHI values with respect to controls both in the morning (0.56 vs. 1.36; P < 0.0001) and in the afternoon (1.12 vs. 1.53; P < 0.0001). In patients, BHI values in the afternoon were significantly higher than in the morning (P < 0.0001). These data demonstrate a diminished vasodilator reserve in OSAS patients, particularly evident in the morning. This reduction of the possibility of cerebral vessels to adapt functionally in response to stimulation could be linked to hyposensitivity of cerebrovascular chemoreceptors after the continuous stress caused by nocturnal hypercapnia.
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PMID:Impairment of daytime cerebrovascular reactivity in patients with obstructive sleep apnoea syndrome. 984 56

Pulmonary barotrauma-induced cerebral arterial gas embolism (CAGE) continues to complicate compressed gas diving activities. Inadequate lung ventilation secondary to inadvertent breath holding or rapid buoyant ascent can quickly generate a critical state of lung over-pressure. Pulmonary over-pressurization may also occur as a consequence of acute and chronic pulmonary pathologies. Resulting barotrauma frequently causes structural failure within the terminal distal airway. Respiratory gases are then free to embolize the systemic circulation via the pulmonary vasculature and the left heart. The brain is a common target organ. Bubbles that enter the cerebral arteries coalesce to form columns of gas as the vascular network narrows. Small amounts of gas frequently pass directly through the cerebral circulation without occlusion. Larger columns of gas occlude regional brain blood flow, either transiently or permanently, producing a stroke-like clinical picture. In cases of spontaneous redistribution, a period of apparent recovery is frequently followed by relapse. The etiology of relapse appears to be multifactoral, and chiefly the consequence of a failure of reperfusion. Prediction of who will relapse is not possible, and any such relapse is of ominous prognostic significance. It is advisable, therefore, that CAGE patients who undergo spontaneous recovery be promptly recompressed while breathing oxygen. Therapeutic compression will serve to antagonize leukocyte-mediated ischemia-reperfusion injury; limit potential re-embolization of brain blood flow, secondary to further leakage from the original pulmonary lesion or recirculation of gas from the initial occlusive event; protect against embolic injury to other organs; aid in the resolution of component cerebral edema; reduce the likelihood of late brain infarction reported in patients who have undergone spontaneous clinical recovery; and prophylax against decompression sickness in high gas loading dives that precede accelerated ascents and omitted stage decompression.
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PMID:Pulmonary barotrauma-induced cerebral arterial gas embolism with spontaneous recovery: commentary on the rationale for therapeutic compression. 1184 83

The alteration of lung volumes in swimmers performing different strokes was the theme of the present study. The study was carried out due to lack of knowledge regarding the lung volumes of different strokers. As the energy expenditure, O2 consumption rate, body movements, viz. arm and leg movements differ with each stroke, the lung function status and mechanics of breathing in swimmers has to cope up with the stroke techniques. Lung volumes, viz. VC, FVC, FEV1 and RVind decrease from resting condition to after swimming performance in freestyle swimmers and butterfly stroke swimmers. The primary reason for the decline in lung volumes after exercise bout, found out from several reports is that it may be due to the fatigue of respiratory muscle. When lung volumes of different swimming strokers were compared with age and height matched controls a higher lung volume were observed in swimmers performing different strokes. Higher breath holding ability of swimmers may facilitate the increase in the strength of respiratory musculature. This may have lead to higher lung volumes in swimmers. From the results of different strokers of swimmers, it is clear that lung volumes differ with respect to the stroke technique employed by the swimmer. Here the age and height, training duration of the swimmers performing different strokes were almost matched, so it is more or less clear that lung volumes are influenced by different swarming strokes. The results of the study can be utilised for the selection trials of swimmers. The study outlines the need for research work in swimmers to be more specific with regard to strokes than generalizing swimmers of different strokes as a category together.
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PMID:Lung volumes in swimmers performing different styles of swimming. 1202 93

Changes in cardiovascular parameters elicited during a maximal breath hold are well described. However, the impact of consecutive maximal breath holds on central hemodynamics in the postapneic period is unknown. Eight trained apnea divers and eight control subjects performed five successive maximal apneas, separated by a 2-min resting interval, with face immersion in cold water. Ultrasound examinations of inferior vena cava (IVC) and the heart were carried out at times 0, 10, 20, 40, and 60 min after the last apnea. The arterial oxygen saturation level and blood pressure, heart rate, and transcutaneous partial pressures of CO(2) and O(2) were monitored continuously. At 20 min after breath holds, IVC diameter increased (27.6 and 16.8% for apnea divers and controls, respectively). Subsequently, pulmonary vascular resistance increased and cardiac output decreased both in apnea divers (62.8 and 21.4%, respectively) and the control group (74.6 and 17.8%, respectively). Cardiac output decrements were due to reductions in stroke volumes in the presence of reduced end-diastolic ventricular volumes. Transcutaneous partial pressure of CO(2) increased in all participants during breath holding, returned to baseline between apneas, but remained slightly elevated during the postdive observation period (approximately 4.5%). Thus increased right ventricular afterload and decreased cardiac output were associated with CO(2) retention and signs of peripheralization of blood volume. These results indicate that repeated apneas may cause prolonged hemodynamic changes after resumption of normal breathing, which may suggest what happens in sleep apnea syndrome.
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PMID:Increased pulmonary vascular resistance and reduced stroke volume in association with CO2 retention and inferior vena cava dilatation. 1672 15

We investigated the spleen volume changes as related to the cardiovascular responses during short-duration apneas at rest. We used dynamic ultrasound splenic imaging and noninvasive photoplethysmographic cardiovascular measurements before, during, and after 15-20 s apneas in seven trained divers. The role of baroreflex was studied by intravenous bolus of vasodilating drug trinitrosan during tidal breathing. The role of lung volume was studied by comparing the apneas at near-maximal lung volume with apneas after inhaling tidal volume, with and without cold forehead stimulation. In apneas at near maximal lung volume, a 20% reduction in splenic volume (P = 0.03) was observed as early as 3 s after the onset of breath holding. Around that time the heart rate increased, the mean arterial pressure abruptly decreased from 89.6 to 66.7 mmHg (P = 0.02), and cardiac output decreased, on account of reduction in stroke volume. Intravenous application of trinitrosan resulted in approximately 6-mmHg decrement in mean arterial pressure, while the splenic volume decreased for approximately 13%. In apneas at low lung volume, the early splenic contraction was also observed, 10% without and 12% with cold forehead stimulation, although the mean arterial pressure did not change or even increased, respectively. In conclusion, the spleen contraction is present at the beginning of apnea, accentuated by cold forehead stimulation. At large, but not small, lung volume, this initial contraction is probably facilitated by downloaded baroreflex in conditions of decreased blood pressure and cardiac output.
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PMID:Spleen and cardiovascular function during short apneas in divers. 1794 4


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