Can resting lung function predict the response of a person living with motor neuron disease to a hypoxic challenge test?

OBJECTIVE

People living with MND (PlwMND) are at risk of altitude-related hypoxia during flight. The Hypoxic Challenge Test (HCT) determines whether in-flight oxygen is required but can be expensive and inaccessible. To assist with travel recommendations, we investigated the relationship between altitude simulation-induced hypoxemia and baseline lung function.

METHODS

Retrospective audit of clinical database of PlwMND who had HCT and lung function. Pearson's correlation assessed relationships between oxygen saturation at altitude (AltSpO2) and lung function. Univariate logistic regression analysis and receiver operator characteristic (ROC) curves determined associations between lung function and HCT pass or fail.

RESULTS

Between 2004-2023, 50 PlwMND were identified (median (IQR) diagnosis to HCT = 11.6 (16.9) months, mean ± SD forced vital capacity (FVC) = 2.4 ± 0.9 liters). Ten patients dropped below 85% SpO2 during testing (HCT fail). Baseline SpO2 was associated with AltSpO2 (r = 0.64) and predicted HCT pass or fail (OR 2.0 [95% CI 1.2-3.4], area under ROC curve (AUC) =0.8 [0.6-1.0]), as did FVC (AUC = 0.8 [0.6-0.9]). PlwMND with a FVC > 2.7L or a resting SpO2 > 97% are likely to pass HCT, whereas all those with FVC < 1L and SpO2 < 92% failed.

CONCLUSION

PlwMND with FVC >2.7L or SpO2 >97% are unlikely to require oxygen or ventilatory supports for airline travel. A FVC below 2.7L will require a HCT to confidently determine HCT outcome, with testing still required for FVC <1L or baseline SpO2 <92%, to provide evidence to the airlines for in-flight respiratory support.

Can Patients Travel by Air Less Than 1 Week After Lung Nodulectomy?

Objective: The study objective was to determine empirically based timing recommendations for safe air travel following lung nodulectomy. Methods: All patients who underwent pulmonary nonanatomic resection followed by air travel home immediately after discharge were identified at 2 institutions between 2014 and 2018. These patients were surveyed via telephone regarding any complications they may have experienced during their travel home and within the first week after discharge. These complications included shortness of breath, chest pain, drainage from their surgical sites, and evaluation by a health care provider in the interim, if they required. Results: Our study identified 27 patients who fit the inclusion criteria. The median number of days between surgery and flight home in the studied population was 4 days. The median number of days between chest tube removal and flight home was 2 days. None of the 27 patients reported experiencing shortness of breath, chest pain, drainage from their surgical sites, or need for evaluation by a health care provider within 1 week of discharge. Nine patients (33%) traveled by air with a small (<5%) pneumothorax documented on chest radiography after removal of thoracostomy tube. One (4%) patient successfully traveled without complication with a 10% pneumothorax. Conclusions: The findings of our study support the safety of air travel following lung nodulectomy in patients who have undergone uneventful wedge resection and have no significant pulmonary or cardiac comorbidities. It is not necessary for patients to wait the recommended 7 days prior to traveling.

Can a patient with pulmonary hypertension travel safely by plane?

Air travel is known as the safest way of transportation. Therefore, patients with health problems prefer to travel by air; however, those with heart or lung issues, who do not have any problems under normal conditions, may experience some problems in high altitude and different environmental conditions. In this review, we have described the points to be considered during air travel in patients with pulmonary hypertension.

Fit for high altitude: are hypoxic challenge tests useful?

Altitude travel results in acute variations of barometric pressure, which induce different degrees of hypoxia, changing the gas contents in body tissues and cavities. Non ventilated air containing cavities may induce barotraumas of the lung (pneumothorax), sinuses and middle ear, with pain, vertigo and hearing loss. Commercial air planes keep their cabin pressure at an equivalent altitude of about 2,500 m. This leads to an increased respiratory drive which may also result in symptoms of emotional hyperventilation. In patients with preexisting respiratory pathology due to lung, cardiovascular, pleural, thoracic neuromuscular or obesity-related diseases (i.e. obstructive sleep apnea) an additional hypoxic stress may induce respiratory pump and/or heart failure. Clinical pre-altitude assessment must be disease-specific and it includes spirometry, pulsoximetry, ECG, pulmonary and systemic hypertension assessment. In patients with abnormal values we need, in addition, measurements of hemoglobin, pH, base excess, PaO₂, and PaCO₂ to evaluate whether O₂- and CO₂-transport is sufficient.

Instead of the hypoxia altitude simulation test (HAST), which is not without danger for patients with respiratory insufficiency, we prefer primarily a hyperoxic challenge. The supplementation of normobaric O₂ gives us information on the acute reversibility of the arterial hypoxemia and the reduction of ventilation and pulmonary hypertension, as well as about the efficiency of the additional O₂-flow needed during altitude exposure. For difficult judgements the performance of the test in a hypobaric chamber with and without supplemental O₂-breathing remains the gold standard. The increasing numbers of drugs to treat acute pulmonary hypertension due to altitude exposure (acetazolamide, dexamethasone, nifedipine, sildenafil) or to other etiologies (anticoagulants, prostanoids, phosphodiesterase-5-inhibitors, endothelin receptor antagonists) including mechanical aids to reduce periodical or insufficient ventilation during altitude exposure (added dead space, continuous or bilevel positive airway pressure, non-invasive ventilation) call for further randomized controlled trials of combined applications.

COPD and air travel: oxygen equipment and preflight titration of supplemental oxygen

BACKGROUND

Patients with COPD may need supplemental oxygen during air travel to avoid development of severe hypoxemia. The current study evaluated whether the hypoxia-altitude simulation test (HAST), in which patients breathe 15.1% oxygen simulating aircraft conditions, can be used to establish the optimal dose of supplemental oxygen. Also, the various types of oxygen-delivery equipment allowed for air travel were compared.

METHODS

In a randomized crossover trial, 16 patients with COPD were exposed to alveolar hypoxia: in a hypobaric chamber (HC) at 2,438 m (8,000 ft) and with a HAST. During both tests, supplemental oxygen was given by nasal cannula (NC) with (1) continuous flow, (2) an oxygen-conserving device, and (3) a portable oxygen concentrator (POC).

RESULTS

PaO(2) kPa (mm Hg) while in the HC and during the HAST with supplemental oxygen at 2 L/min (pulse setting 2) on devices 1 to 3 was (1) 8.6 ± 1.0 (65 ± 8) vs 12.5 ± 2.4 (94 ± 18) (P < .001), (2) 8.6 ± 1.6 (64 ± 12) vs 9.7 ± 1.5 (73 ± 11) (P < .001), and (3) 7.7 ± 0.9 (58 ± 7) vs 8.2 ± 1.1 (62 ± 8) (P= .003), respectively.

CONCLUSIONS

The HAST may be used to identify patients needing supplemental oxygen during air travel. However, oxygen titration using an NC during a HAST causes accumulation of oxygen within the facemask and underestimates the oxygen dose required. When comparing the various types of oxygen-delivery equipment in an HC at 2,438 m (8,000 ft), compressed gaseous oxygen with continuous flow or with an oxygen-conserving device resulted in the same PaO(2), whereas a POC showed significantly lower PaO(2) values.

TRIAL REGISTRY

ClinicalTrials.gov; No.: Identifier: NCT01019538; URL: clinicaltrials.gov.

Decreased steady-state cerebral blood flow velocity and altered dynamic cerebral autoregulation during 5-h sustained 15% O2 hypoxia

Effects of hypoxia on cerebral circulation are important for occupational, high-altitude, and aviation medicine. Increased risk of fainting might be attributable to altered cerebral circulation by hypoxia. Dynamic cerebral autoregulation is reportedly impaired immediately by mild hypoxia. However, continuous exposure to hypoxia causes hyperventilation, resulting in hypocapnia. This hypocapnia is hypothesized to restore impaired dynamic cerebral autoregulation with reduced steady-state cerebral blood flow (CBF). However, no studies have examined hourly changes in alterations of dynamic cerebral autoregulation and steady-state CBF during sustained hypoxia. We therefore examined cerebral circulation during 5-h exposure to 15% O2 hypoxia and 21% O2 in 13 healthy volunteers in a sitting position. Waveforms of blood pressure and CBF velocity in the middle cerebral artery were measured using finger plethysmography and transcranial Doppler ultrasonography. Dynamic cerebral autoregulation was assessed by spectral and transfer function analysis. As expected, steady-state CBF velocity decreased significantly from 2 to 5 h of hypoxia, accompanying 2- to 3-Torr decreases in end-tidal CO2 (ETCO2). Furthermore, transfer function gain and coherence in the very-low-frequency range increased significantly at the beginning of hypoxia, indicating impaired dynamic cerebral autoregulation. However, contrary to the proposed hypothesis, indexes of dynamic cerebral autoregulation showed no significant restoration despite ETCO2 reductions, resulting in persistent higher values of very-low-frequency power of CBF velocity variability during hypoxia (214 ± 40% at 5 h of hypoxia vs. control) without significant increases in blood pressure variability. These results suggest that sustained mild hypoxia reduces steady-state CBF and continuously impairs dynamic cerebral autoregulation, implying an increased risk of shortage of oxygen supply to the brain.