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PubMed2001

Dysregulation of peripheral and central chemoreflex responses in Chagas' heart disease patients without heart failure.

BACKGROUND: The peripheral and central chemoreflexes are important autonomic mechanisms for regulating breathing and cardiovascular function. Although pathological inflammatory infiltration of the peripheral chemoreceptors and central nervous system has been reported in Chagas' disease, functional evaluation of chemoreflexes has not yet been performed. METHODS AND RESULTS: The hypothesis that chemoreflex function is altered in patients with Chagas' heart disease (CH) but normal left ventricle function was tested in 12 CH patients and 13 matched control subjects. The ventilatory rate, minute ventilation, heart rate, mean arterial pressure, forearm blood flow, forearm vascular resistance, and venous norepi-nephrine responses to hypoxia and hypercapnia were determined. During hypoxia, the decrease in oxygen saturation was smaller in CH patients, despite a similar ventilatory response between groups. Both groups showed an increase in heart rate during hypoxia, but this response was blunted in CH patients. Although the mean arterial pressure response to hypoxia was similar in both groups, forearm vascular resistance significantly decreased in control subjects while remaining unchanged in CH patients. Moreover, a significant increase in plasma norepinephrine levels elicited by stimulation of peripheral chemoreceptors was observed only in the CH group. During hypercapnia, the increase in minute ventilation was smaller in CH patients, who did not exhibit the increase in norepinephrine observed in control subjects. CONCLUSIONS: These data suggest that CH potentiates respiratory, cardiovascular, and autonomic responses to peripheral chemoreceptor activation by hypoxia in patients with normal left ventricular function. The ventilatory and sympathetic responses to central chemoreceptor activation by hypercapnia, however, are significantly blunted.

Adult↗
PubMed2001

Cerebral vasoconstriction in vasovagal syncope: any link with symptoms? A transcranial Doppler study.

BACKGROUND: Cerebral vasoconstriction has been described previously in vasovagal syncope (VVS). This phenomenon appears paradoxical in view of the well-known decrease of systemic vascular resistances taking places during VVS. We aimed to assess (1) whether cerebral vasoconstriction in VVS is an independent paradoxical phenomenon and (2) whether cerebral vasoconstriction has any link with symptoms and/or VVS onsets. METHODS AND RESULTS: Seven young patients with recurrent VVS participated in the study. Each patient underwent monitoring of heart rate, blood pressure, cerebral blood flow velocity (by means of transcranial Doppler), end-tidal PCO(2), peripheral oximetry, respiratory rate, and tidal volumes both at rest and during head-up tilt. All the subjects experienced tilt-induced VVS. A significant increase of respiratory tidal volumes was observed in each subject >/=160 seconds before VVS. This deep breathing induced a PCO(2) decrease and, consequently, also a decrease in cerebral blood flow velocity and increase in cerebrovascular resistance (expressed by the increase of the pulsatility index). Within 40 seconds, 5 subjects started complaining of discomfort, in the absence of any significant blood pressure drop. CONCLUSIONS: Cerebral vasoconstriction is not a paradoxical phenomenon when it occurs before tilt-induced VVS but rather is only the physiological consequence of the hyperventilation-induced hypocapnia that occurs in habitual fainters. The large lag between the onset of syncope and cerebral vasoconstriction excludes the hypothesis that VVS is dependent on abnormal behavior of cerebral hemodynamics.

Adolescent↗
PubMed1997

Physiologic benefits of exercise training in rehabilitation of patients with severe chronic obstructive pulmonary disease.

We determined the effect on exercise tolerance and physiological exercise responses of rigorous rehabilitative exercise training in chronic obstructive pulmonary disease (COPD). Fifteen men and 10 women (mean age, 68 +/- 6 yr; FEV1, 0.93 +/- 0.27 L) participated in a rehabilitation program with an exercise component of three per week 45-min sessions of cycle ergometer training for 6 wk with exercise intensity kept near maximal targets. Before and after rehabilitation, patients performed an incremental test and a constant work rate (CWR) test at 80% of the peak work rate in the preprogram incremental test. Ventilation (V(E)) and gas exchange were measured breath by breath; arterialized venous blood was analyzed for blood gas determinations and lactate. Rehabilitation yielded an average increase in peak work rate in the incremental test of 36% (p < 0.001), and in the duration of the CWR test of 77% (p < 0.001). In the CWR test, the kinetics of O2 uptake, CO2 output, V(E), and heart rate were markedly slower than those of healthy subjects. After training, mean response time decrease averaged 17, 22, 34, and 29%, respectively (p < 0.02), evidence of a physiologic training effect. Further, for identical CWR tasks, V(E) was 10% lower (p < 0.02) after training, attributable to altered breathing pattern: tidal volume increased by 8% and respiratory rate decreased by 19%, yielding lower V(D) /V(T) (0.46 versus 0.53 p < 0.005). Rigorous exercise training for patients with severe COPD yields more efficient exercise breathing pattern and lower V(E); this is associated with improved exercise tolerance.

Aged↗
PubMed1998

Measurement of endogenous nitric oxide in the lungs of patients with the acute respiratory distress syndrome.

Elevated levels of nitric oxide (NO) are detectable in the exhaled breath of patients suffering from a number of inflammatory lung diseases. We hypothesized that NO would be detectable in the exhaled air of patients with the acute respiratory distress syndrome (ARDS) undergoing mechanical ventilation and that the concentration would be greater than that from a control group of ventilated subjects. The concentration of NO in the lower airways of 13 patients with ARDS and 18 patients anesthetized and ventilated prior to cardiac surgery was measured by chemiluminescence. The NO concentration was 1.13 +/- 0.36 (mean +/- SEM) parts per billion (ppb) in the ARDS group and 5.5 +/- 0.8 ppb in the control group (2 p < 0.0001). NO is detectable in the exhaled air of patients with ARDS and is at a lower concentration than in control subjects.

Adolescent↗
PubMed1998

Sublingual capnometry for diagnosis and quantitation of circulatory shock.

We investigated sublingual tissue PCO2 during hemorrhagic and septic shock. Hemorrhagic shock was induced in 10 rats. Sublingual PCO2 increased from 45 to 125 mm Hg and arterial pressure declined from 138 to 49 mm Hg, end-tidal PCO2 decreased from 35 to 13 mm Hg, and cardiac index fell from 290 to 77 ml/min/kg. Arterial blood lactate increased from 0.9 to 15.8 mmol/L. Gastric PCO2 was measured in five animals and it increased from 46 to 87 mm Hg. No significant changes were observed in eight "sham" bled animals including the five animals in which gastric PCO2 was measured. Highly significant linear correlations (p < 0.001) between sublingual PCO2 and gastric PCO2 (r = 0.71), cardiac index (r = -0.74), and arterial lactate (r = 0.59) were documented. We subsequently investigated sublingual PCO2 in five animals in which sepsis was induced by intravenous infusion of live Staphylococcus aureus. Like hemorrhagic shock, highly significant linear correlations were observed between end-tidal PCO2 and cardiac index and between sublingual PCO2 and arterial blood lactate. Sublingual PCO2 promises to serve as a technically simple, noninvasive, and rapid response quantitator of severity of circulatory shock states.

Animals↗
PubMedDate not supplied

Accuracy of 30-minute indirect calorimetry studies in predicting 24-hour energy expenditure in mechanically ventilated, critically ill patients.

BACKGROUND: There is no consensus regarding the optimal duration of measurement or time of day to perform indirect calorimetry (IC). Energy expenditure (EE) varies at different times of day and with different activity levels. We sought to assess the variability of EE in mechanically ventilated patients over a 24-hour period and the accuracy of 30-minute IC studies in predicting the 24-hour energy expenditure (EE24). METHODS: The study was a prospective comparison between the resting EE obtained by 30-minute measurement of IC and EE values obtained from 24-hour measurements. Tests were performed in the Medical Intensive Care Unit (MICU) of a tertiary care, university hospital. Oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured for 24 hours in eight ventilated patients. Measurements were made every 3 minutes and used to calculate 30-minute and 24-hour oxygen consumption values. EE24 was calculated using the modified Weir equation. Each 30-minute interval was compared with the value obtained from the 24-hour measurement. RESULTS: Three hundred forty-one of 384 30-minute intervals remained for analysis. Average EE24 measured was 1490 +/- 486 kcal/d. Average EE24 predicted by extrapolation from 30-minute studies was 1501 +/- 503 kcal/d, with a mean difference of 0 +/- 209 kcal/d from the measured 24-hour values (range: -1068 to +585 kcal/d). Thirty-minute studies were within 20% of 24-hour measurements for 89% of intervals. The difference between 24-hour and 30-minute studies correlated with changes in minute ventilation (VE), heart rate, systolic blood pressure, and breath rate from their 24-hour means (p < .001). The mean error of EE estimate was greatest between 3 and 11 PM (p < .001). CONCLUSIONS: We conclude the following: (1) EE in MICU patients is variable; (2) 30-minute IC studies predict measured EE24 acceptably well for clinical purposes; and (3) accuracy is maximized if a 30-minute study is performed between 11 PM and 3 PM, and when Ve, heart rate, systolic blood pressure, and breath rate are near the day's average.

Adult↗
PubMed2000

A comparison of carbon dioxide monitoring and oxygenation between facemask and divided nasal cannula.

The divided nasal cannula is a device recently released in Australia that couples oxygen delivery and end-tidal carbon dioxide (PETCO2) monitoring. This study compares the accuracy of PETCO2 measurements by the divided nasal cannula and those measured by a modified facemask (as currently used in this institution), with arterial partial pressure of carbon dioxide (PaCO2). In this crossover study, 30 patients who had arterial lines as part of their routine monitoring were given oxygen via nasal cannula and facemask preoperatively. The PETCO2 was measured with each device and a simultaneous PaCO2 and PaO2 measured after equilibration. The results demonstrate a significant difference between the PETCO2 as measured by each technique. The divided nasal cannula more accurately reflects PaCO2 (mean arterial to end expired gradient of 5 mmHg) and provides a more representative trace when compared to a traditional facemask system. Both methods provided adequate oxygenation.

Capnography↗
PubMed2004

The use of end-tidal carbon dioxide monitoring to confirm endotracheal tube placement in adult and paediatric intensive care units in Australia and New Zealand.

The use of end-tidal carbon dioxide monitoring to assist in confirming endotracheal tube placement is currently not mandatory in intensive care units (ICUs) in Australia and New Zealand. Early detection of failed tracheal intubation is vital to optimize management and to prevent complications. Questionnaires were sent to the lead clinician/head of department of all 66 intensive care units approved for training purposes by the Joint Faculty of Intensive Care Medicine in Australia and New Zealand. The methods used to confirm correct endotracheal tube placement, the availability of end-tidal carbon dioxide monitoring and its role in confirming endotracheal tube placement in the intensive care unit were explored. Completed questionnaires were received from 61 of the 66 centres (92.4%). Wide variation in the method of confirmation of endotracheal tube position was demonstrated, with 23 (37.7%) of units using sub-optimal methods. Sixty (98.3%) of units had end-tidal carbon dioxide monitoring available. Thirty-eight (62%) units shared monitors between several beds; and 22 (36%) had one monitor per bed. End-tidal carbon dioxide monitoring was used routinely to confirm endotracheal tube placement in 42 (68.8%) units. Fifty-two respondents (83.3%) felt that end-tidal carbon dioxide monitoring was superior to other methods for confirming endotracheal tube placement in critically ill patients. Thirty-eight respondents (62.3%) thought that end-tidal carbon dioxide monitoring should be mandatory to confirm tracheal intubation in the intensive care unit. If it were available, 42 respondents (68.8%) would use end-tidal carbon dioxide monitoring for confirmation of every intubation. Mandatory end-tidal carbon dioxide confirmation of endotracheal tube placement was policy in 33 (54.1%) of the intensive care units.

Australia↗
PubMed2005

The relationship between oxygenator exhaust P(CO2) and arterial P(CO2) during hypothermic cardiopulmonary bypass.

During cardiopulmonary bypass the partial pressure of carbon dioxide in oxygenator arterial blood (P(a)CO2) can be estimated from the partial pressure of gas exhausting from the oxygenator (P(E)CO2). Our hypothesis is that P(E)CO2 may be used to estimate P(a)CO2 with limits of agreement within 7 mmHg above and below the bias. (This is the reported relationship between arterial and end-tidal carbon dioxide during positive pressure ventilation in supine patients.) During hypothermic (28-32 degrees C) cardiopulmonary bypass using a Terumo Capiox SX membrane oxygenator, 80 oxygenator arterial blood samples were collected from 32 patients during cooling, stable hypothermia, and rewarming as per our usual clinical care. The P(a)CO2 of oxygenator arterial blood at actual patient blood temperature was estimated by temperature correction of the oxygenator arterial blood sample measured in the laboratory at 37 degrees C. P(E)CO2 was measured by connecting a capnograph end-to-side to the oxygenator exhaust outlet. We used an alpha-stat approach to cardiopulmonary bypass management. The mean difference between P(E)CO2 and P(a)CO2 was 0.6 mmHg, with limits of agreement (+/-2 SD) between -5 to +6 mmHg. P(E)CO2 tended to underestimate P(a)CO2 at low arterial temperatures, and overestimate at high arterial temperatures. We have demonstrated that P(E)CO2 can be used to estimate P(a)CO2 during hypothermic cardiopulmonary bypass using a Terumo Capiox SX oxygenator with a degree of accuracy similar to that associated with the use of end-tidal carbon dioxide measurement during positive pressure ventilation in anaesthetized, supine patients.

Blood Gas Analysis↗
PubMed1997

A simple method for the continuous noninvasive estimate of cardiac output using the Maxima breathing system. A pilot study.

The Maxima is a new breathing system which makes it possible to monitor cardiac output (Q) noninvasively and to follow trends continuously. When used as a rebreathing system in controlled ventilation, the Maxima selectively eliminates alveolar gas and no fresh gas (VF) is eliminated. Without the need for a mixing chamber, eliminated CO2 (FeCO2) may be measured directly. With steady state conditions, and assuming a respiratory quotient of 1, carbon dioxide production (VCO2) = VF x FeCO2. The indirect Fick principle applied to CO2 exchange (Q = VCO2/ venous-to-arterial CO2 content difference (CaCO2-CvCO2) may be modified to Q = VF x FeCO2/(CaCO2-CvCO2). If VF in the breathing system is adjusted so that FeCO2 is equal to CaCO2-CvCO2, then Q = VF. It was found that, in the presence of a normal haemoglobin (13.3 g.dl-1), Q = VF when VF was adjusted to achieve an FeCO2 value of approximately 4.1%. Cardiac output estimates were compared with those obtained using a thermodilution technique in five patients undergoing coronary artery bypass grafting and in four patients with septicaemia in the ICU. Cardiac outputs were estimated from 1. VCO2 measurements and then 2. VCO2 and haemoglobin (Hb). The result of 28 measurements on nine patients with methods 1. and 2. respectively yielded a correlation with thermodilution measurements: coefficient r = 0.91 and 0.94 with a bias of -10.5% and -0.05% and an accuracy of 14% and 9%.

Capnography↗
PubMed1997

Continuous measurement of arterial and end-tidal carbon dioxide during cardiac surgery: Pa-ETCO2 gradient.

There have been reports of a negative arterial to end-tidal CO2 gradient (Pa-ETCO2) during cardiac surgery, so we used capnometry and an intravascular blood gas sensor (Paratrend 7) to continuously monitor this gradient in 20 cardiac surgical patients. We also compared the values obtained from this sensor with those obtained from a standard blood gas analyser at seven time points. We found a significant change in Pa-ETCO2 after cardiopulmonary bypass (P < 0.001) though we were unable to demonstrate a negative Pa-ETCO2 at any time (95% CI 0-14%). There was clinically acceptable agreement between laboratory and Paratrend 7 measurements during and after cardiac surgery.

Aged↗
PubMed1999

Physiological deadspace during normocapnic ventilation under anaesthesia.

Respiratory physiological deadspace (VDphys) during normocapnic ventilation under anaesthesia was studied in 253 patients scheduled for elective non-thoracic surgery. Subjects were ventilated with SERVO 900B ventilator using CO2 analyser 930 (Siemens-Elema Sweden) to adjust minute volume sufficient to maintain end-tidal carbon dioxide fraction (FECO2) around 5.5kPa with normocapnic confirmation using arterial blood gas analysis. VDphys was calculated using Enghoff's modification of Bohr's equation. VDphys and deadspace to tidal volume ratios (VD/VT) in male patients were 142.6 +/- 28.4 ml and 0.37 +/- 0.068 respectively and were significantly higher than that in females (119.4 +/- 35.6 ml and 0.36 +/- 0.067). Males had significantly higher VDphys/mass (2.5 +/- 0.68 ml.kg) compared with females (2.2 +/- 0.54 ml/kg, P < 0.001) but significantly lower body mass index (BMI) (20.67 +/- 3.2 in males and 22.47 +/- 4.1 in females, P < 0.001). VDphys showed positive correlation with weight, height and body surface area (BSA) but VDphys/kg showed negative correlation with BMI. Multiple regression analysis produced a best fit equation for VDphys = 9.7 + 64.3 x BSA + 13.51S where S = 1 for females and 2 for males.

Adolescent↗
PubMedDate not supplied

Noninvasive monitoring of carbon dioxide in infants and children with congenital heart disease: end-tidal versus transcutaneous techniques.

End-tidal CO2 (ET(CO2)) monitoring and transcutaneous (TC) CO2 monitoring were prospectively compared in 53 patients, 1 month to 16 years of age, with congenital heart disease (CHD). There were 32 patients with cyanotic CHD and 21 with acyanotic CHD. The TC-Pa(CO2) difference was 2 +/- 1 mm Hg and the ET-Pa(CO2) difference was 5 +/- 3 mm Hg (P < .0001). The TC-Pa(CO2) difference was < or = 2 mm Hg in 30 of 53 patients and < or = 5 mm Hg in 53 of 53 patients. The ET-Pa(CO2) difference was < or = 2 mm Hg in 9 of 53 patients and < or = 5 mm Hg in 30 of 53 patients (P < .001). No variation in the TC-Pa(CO2) difference was noted based on the type of CHD (acyanotic vs cyanotic) or age. The ET-Pa(CO2) difference was greater in patients with cyanotic versus acyanotic CHD (7 +/- 3 mm Hg vs 4 +/- 2 mm Hg, P < .0001) and in patients < or = 1 year of age versus patients > or = 1 year of age (6 +/- 3 mm Hg vs 4 +/- 2, P = .008). In infants and children with CHD, TC monitoring provides a more accurate estimation of Pa(CO2) than ET monitoring.

Adolescent↗
PubMed2002

Minimizing fire risk during eye surgery.

Supplemental oxygen under the drapes in high concentrations can lead to fires in ophthalmic theaters. This study attempted to eliminate the fire risk while maintaining the required therapeutic effect. The sample consisted of 201 patients undergoing ophthalmic surgery, with 104 subjects in the control group and 97 in the experimental group. A quasi-experimental design compared the existing method of oxygen administration (100% supply) with a new method (experimental) providing 24% oxygen supply. Measurements of the oxygen concentration were taken along with the fractional inspiratory carbon dioxide (FiCO2), the peripheral oxygen saturation (SpO2), the end tidal carbon dioxide (ETCO2), and the respiratory rate (RR). There was a significant difference in oxygen and carbon dioxide concentrations under the drapes (p <.05). The fractional inspiratory carbon dioxide was reduced in the experimental group. The new method was adopted to reduce the risk of fire in ophthalmic operating theaters.

Adolescent↗
PubMed1997

Unsteadiness of breathing in patients with hyperventilation syndrome and anxiety disorders.

The breathing pattern of 399 patients with hyperventilation syndrome (HVS) and/or with anxiety disorders and that of 347 normal controls was investigated during a 5 min period of quiet breathing and after a 3 min period of voluntary hyperventilation. The diagnosis of HVS was based on the presence of several suggestive complaints occurring in the context of stress, and reproduced by voluntary hyperventilation. Organic diseases as a cause of the symptoms were excluded. The anxiety disorders were diagnosed by means of an abbreviated version of the Anxiety Disorders Interview Schedule (ADIS). There was a large overlap between the two diagnoses. Simply breathing via a mouthpiece and pneumotachograph made end-tidal CO2 fractional concentration (FET,CO2) decrease progressively both in hyperventilators and in patients with anxiety disorders, but not in normals. At the start of the measurement the FET,CO2 was not different between patients and healthy subjects. In patients < or = 28 yrs, the decrease of FET,CO2 resulted from a higher tidal volume, and in patients > or = 29 years from an increase in frequency. After voluntary hyperventilation, the recovery of FET,CO2, was delayed in patients, due to a slower normalization of respiratory frequency in females and in older males, and of tidal volume in younger males, and also due to less frequent end-expiratory pauses. When breathing was recorded first by means of inductive plethysmography (Respitrace), the progressive decline of FET,CO2 seen in patients was not observed: from the onset of the recording, FET,CO2 was reduced in patients. It did not change further when, immediately afterwards, the subject switched to mouthpiece breathing. The finding that breathing through a mouthpiece induces hyperventilation in patients and that recovery of FET,CO2 is delayed after voluntary hyperventilation, suggests that the respiratory control system is less resistant to challenges (mouthpiece or voluntary hyperventilation) in those patients. On the other hand, the lower values of FET,CO2 measured during recording by means of a Respitrace probably result from a challenge, prior to the recordings, induced by the fitting of the measuring device to the patient. This unsteadiness of breathing characterizes patients with hyperventilation syndrome and those with anxiety disorders, but is not sufficiently sensitive to be used for individual diagnosis.

Adult↗
PubMed1997

Exercise performance in children with asthma: is it different from that of healthy controls?

Exercise tolerance and possible limitation in work capacity of asthmatic children is still a matter of debate. The aim of this study was to compare ventilation and gas exchange response to exercise of asthmatic children with that of healthy controls. Exercise performance was evaluated in 80 children with mild-to-moderate asthma, aged 7-15 yrs, and in 80 healthy controls matched for age, height, weight and habitual level of physical activity. The children performed a maximal exercise test on a treadmill, during which oxygen uptake (V'O2), carbon dioxide output (V'CO2) and minute ventilation (V'E) were measured continuously. No premedication was given to the asthmatic children. Forced expiratory volume in one second (FEV1) at rest was 93+/-11% of predicted in asthmatic children and 95+/-9% pred in controls. After the run, the mean fall in FEV1 was 13.9% (range 0-57%) and 1.6% (0-9%), respectively (p<0.001). The two groups achieved similar maximum oxygen uptake (V'O2,max) ((mean+/-SD) 40.3+/-8.4 and 42.6+/-9.6 mL x min(-1) x kg(-1) in asthmatics and controls, respectively; NS) and maximum minute ventilation output (V'E,max) (42.9+/-14.8 and 45.7+/-14.9 L x min(-1) respectively; NS). The kinetics of V'O2, V'CO2 and V'E during the test revealed no differences between the two populations. Moreover, anaerobic threshold and oxygen pulse were the same in the two groups. Asthmatics showed a ventilatory pattern with lower respiratory frequencies and greater tidal volumes during the run. These results suggest that asthmatic children can achieve a level of exercise performance similar to that of healthy children, provided that they have a comparable level of habitual physical activity. The only difference found concerned the ventilatory pattern of the asthmatic children, which was characterized by a reduced respiratory frequency and greater tidal volume at the same minute ventilation. The level of physical conditioning was found to be the main determinant of exercise tolerance for children with controlled asthma.

Adolescent↗