Alveolar partial pressures of carbon dioxide and oxygen measured by a helium washout technique.

Steady-state simulation of the human respiratory system

Blood flow compensates oxygen demand in the vulnerable ca3 region of the hippocampus during kainate-induced seizures

Continuous determination of the cerebrovascular changes induced by bicuculline and kainic acid in unanaesthetized spontaneously breathing rats

Partial pressures of oxygen and carbon dioxide in bone and their correlation with bone‐blood flow: Effect of decreased arterial supply and venous congestion on intraosseous oxygen and carbon dioxide in an animal model

Measurement of Cardiac Output during Exercise

Tribukait, B. Arterielle O2Hb‐Sättigung und alevolarer CO2 and O2 Druck der Ratte bei Aufenthalt in 2000—7000 m Höhe. Acta physiol. stand. 1963. 58. 90—98. — Rats were subjected to hypoxia corresponding to an altitude of 2,000—7,000 m. The oxygen saturation in arterial blood of anesthetized animals was determined by the van Slyke method. For determination of alveolar carbon dioxide and oxygen tensions unanesthetized animals were kept in a closed breathing system, to which a small amount of carbon monoxide was added. From the pressures of oxygen and carbon monoxide in this system, and the COHb and O2Hb saturations together with the alveolar gas equations, the alveolar carbon dioxide and oxygen pressures were calculated. The O2Hb saturation decreased from 91% at sea level to 83, 65, 56 and 39% at 2,000, 4,000, 6,000 and 7,000 m altitude respectively. The calculated carbon dioxide pressures decreased from a predicted value of 40 mm Hg at sea level to 35, 32, 17 and 14 mm Hg at 2,000, 4,000, 6,000 and 7,000 m altitude respectively. These values for CO2‐tensions are in general agreement with those observed in man.

1717 Numerous studies have reported little correlation between exercise capacity and resting indices of ventricular function in congestive heart failure (CHF). In 12 stable CHF patients (45.8±6.9 yrs; left ventricular ejection fraction 18.5±4.5% assessed by echocardiography) the maximum exercise capacity (70.4±19.9 Watts) and the maximum heart rate (HR) were determined in an upright cycle ergometry. Partial pressures of oxygen (PO2) and carbon dioxide (PCO2), and lactate concentrations (LA) were measured in capillary blood at rest (RE) and until exhaustion (EX). Minute ventilation (VE), carbon dioxide production (VCO2), oxygen consumption (VO2) and respiratory exchange ratio (RQ) were determined spirometrically. (Table)TableThe insignificantly changes of PO2 and PCO2 during the exercise test contradicts a limitation in pulmonary gas exchange. Nevertheless, the peak oxygen consumption (VO2 peak: 15.7±2.96mL/kg/min) was critically reduced. The findings suggest that besides the impaired pump capacity of the heart a reduced aerobic activity of the skeletal muscle plays an important role in restricting the VO2peak in CHF patients.

Influence of energy substrates on respiratory gas exchange during conventional mechanical ventilation of preterm infants

Xylazine, midazolam and a midazolam/ketamine combination were administered to 6 goats in a randomised 3-way block design. All goats received all treatments with at least a 7-day interval between treatments. Statistically significant (P < 0.05) changes were observed in some of the measured cardiopulmonary variables for xylazine and midazolam/ ketamine. Xylazine administration resulted in statistically significant decreases in minute volume, arterial partial pressure of oxygen, heart rate and mean arterial blood pressure. The increase in arterial partial pressure of carbon dioxide was not statistically significant. For the midazolam/ketamine combination, the decrease in tidal volume was statistically significant, but not the decrease in minute volume and increase in arterial partial pressure of carbon dioxide. The decrease in the arterial partial pressure of oxygen was also statistically significant. The mean arterial blood pressure for the combination was statistically significantly higher compared to xylazine. The changes in cardiopulmonary variables after midazolam administration were not statistically significant, such as tidal and minute volume, arterial partial pressure of oxygen and carbon dioxide. However, clinically significant effects such as hypoventilation and hypoxia were observed after its administration. The change in mean arterial blood pressure was minimal.

Assessment of oxygenation is fundamental to the care of patients. Numerous indices of oxygenation have been developed that entail variable degrees of invasiveness, complexity and physiologic underpinning. The clinical reliability of these indices has been questioned. This theoretical study uses a steady-state model of blood gas physiology to study the assumptions and nonpulmonary factors that have been hypothesized to impact index performance. A model derived from cardiac and pulmonary Fick expressions was used to calculate the effects of the physiological parameters-shunt, dead space, cardiac output, ventilation, oxygen extraction, carbon dioxide elimination, hematocrit, temperature and base excess-on predicted arterial, mixed-venous and post-capillary oxygen contents and arterial and alveolar oxygen and carbon dioxide partial pressures. Values of these parameters were determined over a range of shunt from 0 to 50% and then used to calculate (1) estimated shunt with the shunt equation and FShunt, and (2) the alveolar-arterial partial pressure of oxygen difference (A-a [Formula: see text] gradient), and the arterial partial pressure of oxygen to fraction of inspired oxygen (Pa/Fi) ratio. Calculations were performed either treating parameters as fixed (assuming several values) or as random variables. Assumptions of constant arterio-venous oxygen content and of alveolar and arterial partial pressures of carbon dioxide being equal were shown to fail in certain settings where shunt and physiologic parameters varied. These effects manifested as calculated indices either over or under-estimating actual shunt by FShunt, or wide unpredictable variability (scatter) when correlating A-a [Formula: see text] gradient and Pa:Fi ratio to actual shunt. Cardiac output and oxygen extraction have noticeable impacts on all calculated indices. The results support the clinical observations that the performance of indices of oxygenation can vary with fraction of inspired oxygen and various nonpulmonary physiological factors that underly heterogeneity present in the clinical population.

Arterial blood gases, oxygen, carbon dioxide, and the potential of hydrogen are the key indicators of respiratory status and should be continuously monitored for patients whose respiratory vital signs may alter frequently and rapidly. The arterial partial pressure of oxygen and carbon dioxide can be estimated with transcutaneous monitoring, which measures the partial pressure of oxygen and carbon dioxide diffusing from the skin. However, requiring a heating element and a large, expensive bedside monitor are the limitations of the traditional transcutaneous blood gas monitors preventing continuous monitoring outside a clinical setting. Therefore, we propose a miniaturized fluorescent thin film-based prototype, envisioned as a first-of-its-kind continuous transcutaneous carbon dioxide monitoring wearable device. The computation principle relies on measuring the fluorescence intensity of a carbon dioxide-sensitive thin film. The prototype monitor estimates the partial pressure of carbon dioxide ranging from 0 to 75 mmHg, covering the clinically significant range, 35–45 mmHg for healthy humans. The prototype is designed with a small form factor on a 60 mm×55 mm printed circuit board and consumes 64.33 mW, suitable to be translated into a wearable device in further design stages.

Puncture of the radial artery is the preferred method of obtaining an arterial blood sample for blood gas analysis. The chief indication for blood gas analysis is the need to obtain values for the partial pressures of oxygen and carbon dioxide and for arterial pH. This information is needed in assessing a patient with acute, severe respiratory distress. Measurements of arterial pH and the partial pressures of carbon dioxide and oxygen provide accurate information on the status of acid–base balance and gas exchange. Another indication for arterial blood gas sampling is the need to perform CO-oximetry in order to assess for methemoglobinemia and carboxyhemoglobinemia. Contraindications Radial arterial puncture is contraindicated in the presence of a known deficiency of collateral circulation to the distal upper extremity. A modified Allen test can be performed to assess the adequacy of the collateral circulation of the radial artery by the ulnar artery (Fig. 1). To perform the test, occlude both the ulnar and radial arteries. Instruct the patient to make a fist to drain the blood from the hand; this should be done for approximately 30 seconds. Instruct the patient to unclench the fist. The patient’s palm should appear blanched or pale. Now, release pressure only from the ulnar artery. Adequate collateral circulation is indicated by the return of normal color within 10 seconds. 1 There is no agreement as to whether the Allen test can accurately predict the risk of rare ischemic complications. 2 On the basis of current evidence, its use can be neither refuted nor supported. Alternative techniques to measure collateral circulation of the forearm include color Doppler studies of flow, plethysmography, and magnetic resonance imaging. 3 These methods are more often used in assessing the radial artery for more invasive procedures, such as arterial harvesting for coronary bypass. Radial arterial puncture should not be performed in patients with an overlying skin infection. In patients who are taking anticoagulants or in those with coagulopathies, it should be performed only if absolutely necessary, because of the increased risk of bleeding and hematoma formation. Preparation Standard kits for sampling arterial blood gas are readily available and should contain a syringe, a small 23-to-25-gauge needle (either with a rubber stopper used to remove the needle from the syringe or with an attached safety cap), and a syringe cap containing dry lithium heparin or sodium heparin. The concentration of hepa

This study aimed to compare the venous acid-base status of healthy awake versus anesthetized Magellanic penguins (Spheniscus magellanicus). Ten nonanesthetized penguins were manually restrained, and a venous blood sample was collected. Six of these penguins were anesthetized by 2% isoflurane and, after an anesthetic stabilization period, both venous and arterial blood samples were simultaneously withdrawn. Using an i-STAT analyzer, partial pressure of carbon dioxide (PCO2), partial pressure of oxygen (PO2), pH, standard bicarbonate concentration (HCO3-), total carbon dioxide (ctCO2), oxygen saturation (SO2), base excess (BE), Na+, and K+ levels were measured in venous blood samples of awake (Gawake) penguins and in venous (Gven) and arterial blood (Gart) samples of anesthetized penguins. There were no significant differences between groups in pH, BE, or Na+. Venous carbon dioxide pressure, HCO3-, and venous ctCO2 were higher in Gven than Gawake penguins, whereas PCO2 was higher in Gven than Gart penguins. PO2 and SO2 were higher in the Gart group than in the other groups. Both venous and arterial blood samples may be used to evaluate the acid-base profile of Magellanic penguins.

OBJECTIVE To assess multiple central venous and arterial blood variables that alone or in conjunction with one another reflect global oxygenation status in healthy neonatal foals. ANIMALS 11 healthy neonatal foals. PROCEDURES Central venous and arterial blood samples were collected from healthy neonatal foals at 12, 24, 36, 48, 72, and 96 hours after birth. Variables measured from central venous and arterial blood samples included oxygen saturation of hemoglobin, partial pressure of oxygen, lactate concentration, partial pressure of carbon dioxide, and pH. Calculated variables included venous-to-arterial carbon dioxide gap, estimated oxygen extraction ratio, ratio of partial pressure of oxygen in arterial blood to the fraction of inspired oxygen, bicarbonate concentration, base excess, and blood oxygen content. RESULTS Significant differences between arterial and central venous blood obtained from neonatal foals were detected for several variables, particularly partial pressure of oxygen, oxygen saturation of hemoglobin, and oxygen content. In addition, the partial pressure of carbon dioxide in central venous blood samples was significantly higher than the value for corresponding arterial blood samples. Several temporal differences were detected for other variables. CONCLUSIONS AND CLINICAL RELEVANCE Results of this study provided information about several variables that reflect global oxygenation in healthy neonatal foals. Values for these variables in healthy foals can allow for comparison with values for critically ill foals in future studies. Comparison of these variables between healthy and ill foals may aid in treatment decisions and prognosis of clinical outcome for critically ill foals.

To investigate the effect of reverse Trendelenburg position versus semi-recumbent position on respiratory parameters of obese critically ill patients. Reverse Trendelenburg position is recommended for obese patients; however, the effect among critically ill patients, especially those on mechanical ventilation, has limited study. Randomised, controlled pretest, repeated post-test trial with two parallel groups. The study started from 13 January 2020-12 March 2020. Adult critically ill patients with a body mass index ≥30 were randomly assigned by computer-generated randomisation to either reverse Trendelenburg position group (intervention) or semi-recumbent position group (active comparator control). Outcome measures were ventilation parameters (dynamic compliance, partial pressure of arterial carbon dioxide and minute volume) and oxygenation parameters (hypoxaemic index and partial pressure of arterial oxygen). Measures were assessed immediately before positioning and after positioning in 10 minutes, 20 minutes and 30 minutes. CONSORT checklist was used to report the current study. Four general intensive care units. One hundred and ten patients (55 patients in each group) completed the study. The reverse Trendelenburg position group had a higher improvement than the semi-recumbent position group as estimated by mean differences in their dynamic compliance, minute volume, partial pressure of carbon dioxide, partial pressure of oxygen and hypoxaemic index. Reverse Trendelenburg position improves obese patients' respiratory parameters more than semi-recumbent position. This study directs nurses to use the reverse Trendelenburg position, which is an important position for enhancing the parameters of ventilation and oxygenation of obese mechanically ventilated patients.