Multiple-day high-dose beetroot juice supplementation does not improve pulmonary or muscle deoxygenation kinetics of well-trained cyclists in normoxia and hypoxia

Dietary nitrate (NO₃^-) supplementation via beetroot juice (BR) has been reported to lower oxygen cost (i.e., increased exercise efficiency) and speed up oxygen uptake (VO₂) kinetics in untrained and moderately trained individuals, particularly during conditions of low oxygen availability (i.e., hypoxia). However, the effects of multiple-day, high dose (12.4 mmol NO_3- per day) BR supplementation on exercise efficiency and VO₂ kinetics during normoxia and hypoxia in well-trained individuals are not resolved. In a double-blinded, randomized crossover study, 12 well-trained cyclists (66.4 ± 5.3 ml min^-1∙kg^-1) completed three transitions from rest to moderate-intensity (~70% of gas exchange threshold) cycling in hypoxia and normoxia with supplementation of BR or nitrate-depleted BR as placebo. Continuous measures of VO₂ and muscle (vastus lateralis) deoxygenation (ΔHHb, using near-infrared spectroscopy) were acquired during all transitions. Kinetics of VO₂ and deoxygenation (ΔHHb) were modeled using mono-exponential functions. Our results showed that BR supplementation did not alter the primary time constant for VO₂ or ΔHHb during the transition from rest to moderate-intensity cycling. While BR supplementation lowered the amplitude of the VO₂ response (2.1%, p = 0.038), BR did not alter steady state VO₂ derived from the fit (p = 0.258), raw VO₂ data (p = 0.231), moderate intensity exercise efficiency (p = 0.333) nor steady state ΔHHb (p = 0.224). Altogether, these results demonstrate that multiple-day, high-dose BR supplementation does not alter exercise efficiency or oxygen uptake kinetics during normoxia and hypoxia in well-trained athletes.

Is venous blood a more reliable description of acid-base state following simulated hypo- and hyperventilation?

Background

ABGs are performed in acute conditions as the reference method for assessing the acid-base status of blood. Hyperventilation and breath-holding are common ventilatory changes that occur around the time of sampling, rapidly altering the ‘true’ status of the blood. This is particularly relevant in emergency medicine patients without permanent arterial catheters, where the pain and anxiety of arterial punctures can cause ventilatory changes. This study aimed to determine whether peripheral venous values could be a more reliable measure of blood gases following acute changes in ventilation.

Methods

To allow for characterisation of ventilatory changes typical of acutely ill patients, but without the confounding influence of perfusion or metabolic disturbances, 30 patients scheduled for elective surgery were studied in a prospective observational study. Following anaesthesia, and before the start of the surgery, ventilator settings were altered to achieve a + 100% or − 60% change in alveolar ventilation (‘hyper-’ or ‘hypoventilation’), changes consistent with the anticipation of a painful arterial puncture commonly encountered in the emergency room. Blood samples were drawn simultaneously from indwelling arterial and peripheral venous catheters at baseline, and at 15, 30, 45, 60, 90 and 120 s following the ventilatory change. Comparisons between the timed arterial (or venous) samples were done using repeated-measures ANOVA, with post-hoc analysis using Bonferroni’s correction.

Results

Arterial blood pH and PCO₂ changed rapidly within the first 15–30s after both hyper- and hypoventilation, plateauing at around 60s (∆pH = ±0.036 and ∆PCO₂ = ±0.64 kPa (4.7 mmHg), respectively), with peripheral venous values remaining relatively constant until 60s, and changing minimally thereafter. Mean arterial changes were significantly different at 30s (P < 0.001) when compared to baseline, in response to both hyper- and hypoventilation.

Conclusion

This study has shown that substantial differences in arterial and peripheral venous acid-base status can be due to acute changes in ventilation, commonly seen in the ER over the 30s necessary to sample arterial blood. If changes are transient, peripheral venous blood may provide a more reliable description of acid-base status.

Model-based measurement of gas exchange in healthy subjects using ALPE essential--influence of age, posture and gender

The ALPE Essential device for model-based measurement of pulmonary gas exchange status may be a useful alternative to current methods for diagnosing, monitoring and evaluating treatment related to pulmonary gas exchange. In this study, shunt and ventilation/perfusion mismatch were measured with ALPE Essential in 106 healthy subjects with the aim of investigating the influence of age, posture and gender on gas exchange parameters and evaluating the test-retest reliability of the measurements. Age and gender did not have statistically significant influence on gas exchange parameters, although there was a tendency for poorer matching of ventilation and perfusion with age. Posture was shown to be important when measuring gas exchange parameters. Absolute measurement reliability was acceptable with future studies in patients being necessary for accurate evaluation of relative reliability.

The effects of oxygen induced pulmonary vasoconstriction on bedside measurement of pulmonary gas exchange

In patients with respiratory failure measurements of pulmonary gas exchange are of importance. The bedside automatic lung parameter estimator (ALPE) of pulmonary gas exchange is based on changes in inspired oxygen (FiO2) assuming that these changes do not affect pulmonary circulation. This assumption is investigated in this study. Forty-two out of 65 patients undergoing coronary artery bypass grafting (CABG) had measurements of mean pulmonary arterial pressure (MPAP), cardiac output and pulmonary capillary wedge pressure thus enabling the calculation of pulmonary vascular resistance (PVR) at each FiO2 level. The research version of ALPE was used and FiO2 was step-wise reduced a median of 0.20 and ultimately returned towards baseline values, allowing 6-8 min' steady state period at each of 4-6 levels before recording the oxygen saturation (SpO2). FiO2 reduction led to median decrease in SpO2 from 99 to 92 %, an increase in MPAP of 4 mmHg and an increase in PVR of 36 dyn s cm(-5). Changes were immediately reversed on returning FiO2 towards baseline. In this study changes in MPAP and PVR are small and immediately reversible consistent with small changes in pulmonary gas exchange. This indicates that mild deoxygenation induced pulmonary vasoconstriction does not have significant influences on the ALPE parameters in patients after CABG.

Measuring gas exchange with step changes in inspired oxygen: an analysis of the assumption of oxygen steady state in patients suffering from COPD

Bedside estimation of pulmonary gas exchange efficiency may be possible from step changes in FIO2 and subsequent measurement of arterial oxygenation at steady state conditions. However, a steady state may not be achieved quickly after a change in FIO2, especially in patients with lung disease such as COPD, rendering this approach cumbersome. This paper investigates whether breath by breath measurement of respiratory gas and arterial oxygen levels as FIO2 is changed can be used as a much more rapid alternative to collecting data from steady state conditions for measuring pulmonary gas exchange efficiency. Fourteen patients with COPD were studied using 4-5 step changes in FIO2 in the range of 0.15-0.35. Values of expired respiratory gas and arterial oxygenation were used to calculate and compare the parameters of a mathematical model of pulmonary gas exchange in two cases: from data at steady state; and from breath by breath data prior to achievement of a steady state. For each patient, the breath by breath data were corrected for the delay in arterial oxygen saturation changes following each change in FIO2. Calculated model parameters were shown to be similar for the two data sets, with Bland-Altman bias and limits of agreement of -0.4 and -3.0 to 2.2 % for calculation of pulmonary shunt and 0.17 and -0.47 to 0.81 kPa for alveolar to end-capillary PO2, a measure of oxygen abnormality due to shunting plus regions of low [Formula: see text] A/[Formula: see text] ratio. This study shows that steady state oxygen levels may not be necessary when estimating pulmonary gas exchange using changes in FIO2. As such this technique may be applicable in patients with lung disease such as COPD.

Can computed tomography classifications of chronic obstructive pulmonary disease be identified using Bayesian networks and clinical data?

Diagnosis and classification of chronic obstructive pulmonary disease (COPD) may be seen as difficult. Causal reasoning can be used to relate clinical measurements with radiological representation of COPD phenotypes airways disease and emphysema. In this paper a causal probabilistic network was constructed that uses clinically available measurements to classify patients suffering from COPD into the main phenotypes airways disease and emphysema. The network grades the severity of disease and for emphysematous COPD, the type of bullae and its location central or peripheral. In four patient cases the network was shown to reach the same conclusion as was gained from the patients' High Resolution Computed Tomography (HRCT) scans. These were: airways disease, emphysema with central small bullae, emphysema with central large bullae, and emphysema with peripheral bullae. The approach may be promising in targeting HRCT in COPD patients, assessing phenotypes of the disease and monitoring its progression using clinical data.

Time to steady state after changes in FIO(2) in patients with COPD

BACKGROUND

International guidelines recommend that when changing FIO2 in patients with COPD receiving Long-Term Oxygen Therapy (LTOT), 30 minutes should be waited for steady state before measurement of arterial blood gasses. This study evaluates whether 30 minutes is really necessary, as a smaller duration might improve the logistics of care, potentially reducing the time spent by patients at the out-patient clinic.

METHODS

12 patients with severe to very severe COPD according to the GOLD guidelines were included. Patients had a median FEV1% of 23% of the predicted value (range 15-64%), median FEV1/FVC 0.43 (range 0.26-0.63), and chronic respiratory failure necessitating LTOT, 1-4 liters/minute, minimum 16 hours/day. Following a FIO2 reduction (wash out), arterial blood gases were measured at 0, 1, 2, 4, 8, 12, 17, 22, 32 and 34 minutes. FIO2 was then increased to baseline levels (wash in) and blood gasses measured at 0, 1, 2, 4, 8, 12, 17, 22, 32, and 34 minutes. Data were analyzed to examine the dynamics of arterial PO2 and saturation (SO2) wash out and wash in by calculating the time constants, tau (ô), and to evaluate the time required to reach values which might be considered clinically stable, defined as PO2 within 0.5 kPa and SO2 within 1% of equilibrium values.

RESULTS

For arterial PO2 values of time constants were about 3 minutes and similar for both wash out and wash in. A median of 5 minutes was required to reach clinically stable values of PO2 in both wash out and wash in, with 7-8 minutes sufficient in 75% of patients, and in the worst case 14 minutes. For SO2, values of the time constant were 4.5 and 1.4 minutes for wash out and wash in, respectively. The time required to reach clinically stable values was different in the two phases. For wash out the median time was 7.4 minutes, and in the worst case 15.6 minutes. For wash in the median time was 2.6 minutes and in worst case 6.8 minutes. No significant changes in PCO2 or pH were seen during FIO2 changes.

DISCUSSION/CONCLUSION

This study shows that oxygen equilibration relevant for clinical interpretation requires only 10 minutes following an increase and 16 minutes following a decrease in FIO2. over the range studied.

Retrospective evaluation of a decision support system for controlled mechanical ventilation

Management of mechanical ventilation in intensive care patients is complicated by conflicting clinical goals. Decision support systems (DSS) may support clinicians in finding the correct balance. The objective of this study was to evaluate a computerized model-based DSS for its advice on inspired oxygen fraction, tidal volume and respiratory frequency. The DSS was retrospectively evaluated in 16 intensive care patient cases, with physiological models fitted to the retrospective data and then used to simulate patient response to changes in therapy. Sensitivity of the DSS's advice to variations in cardiac output (CO) was evaluated. Compared to the baseline ventilator settings set as part of routine clinical care, the system suggested lower tidal volumes and inspired oxygen fraction, but higher frequency, with all suggestions and the model simulated outcome comparing well with the respiratory goals of the Acute Respiratory Distress Syndrome Network from 2000. Changes in advice with CO variation of about 20% were negligible except in cases of high oxygen consumption. Results suggest that the DSS provides clinically relevant and rational advice on therapy in agreement with current 'best practice', and that the advice is robust to variation in CO.