Cheek support affects lung mechanics measurements of tidal-based spontaneous breathing

BACKGROUND AND OBJECTIVE

Patients are required to support their cheeks during breath-occluding lung function tests. This prevents cheek expansion which would alter pressure measured at the mouth, and, consequently, lung mechanics measurements. To date, the effect of cheek support on airway resistance measurements has been assessed. However other lung mechanics have not been studied as thoroughly, and no algorithm to account for the effect of missing cheek support on lung mechanics measurements has been developed.

METHODS

Lung mechanics were assessed with a breath occlusion test during light panting in healthy subjects with and without cheek support in a body plethysmograph. Average model-based airway resistance, lung elastance, and a parameter representing the viscoelastic were measured. Results were compared to quantify the effect of cheek support on these three parameters.

RESULTS

In the nine healthy subjects (5 Female, 4 Male) recruited for this study, all mechanics tended to be underestimated when cheeks were unsupported. Changes in elastance, resistance, and viscoelastic parameter ranged between 1.6-66.8 %, -4.5-21.8 %, and -4.7-68.2 %, respectively, when cheek support was added. The underestimation was due to reduced mouth pressure during cheek expansion when the breath was occluded. The variance of lung mechanics parameters did not change with cheek support in all subjects.

CONCLUSIONS

The error in lung mechanics measurement caused by unsupported cheeks was subject dependent. Hence, no rule-of-thumb could be identified to reconstruct missing cheek support. For correct lung mechanics measurements during breath-occluding lung tests, patients must have adequate cheek support.

ABBREVIATIONS

ROCC: Occlusion resistance; COPD: Chronic Obstructive Pulmonary Disorder; SB: spontaneous breathing.

Inspiratory respiratory mechanics estimation by using expiratory data for reverse-triggered breathing cycles

BACKGROUND AND OBJECTIVE

Model-based lung mechanics monitoring can provide clinically useful information for guiding mechanical ventilator treatment in intensive care. However, many methods of measuring lung mechanics are not appropriate for both fully and partially sedated patients, and are unable provide lung mechanics metrics in real-time. This study proposes a novel method of using lung mechanics identified during passive expiration to estimate inspiratory lung mechanics for spontaneously breathing patients.

METHODS

Relationships between inspiratory and expiratory modeled lung mechanics were identified from clinical data from 4 fully sedated patients. The validity of these relationships were assessed using data from a further 4 spontaneously breathing patients.

RESULTS

For the fully sedated patients, a linear relationship was identified between inspiratory and expiratory elastance, with slope 1.04 and intercept 1.66. The r value of this correlation was 0.94. No cohort-wide relationship was determined for airway resistance. Expiratory elastance measurements in spontaneously breathing patients were able to produce reasonable estimates of inspiratory elastance after adjusting for the identified difference between them.

CONCLUSIONS

This study shows that when conventional methods fail, typically ignored expiratory data may be able to provide clinicians with the information needed about patient condition to guide MV therapy.

A virtual patient model for mechanical ventilation

BACKGROUND AND OBJECTIVES

Mechanical ventilation (MV) is a primary therapy for patients with acute respiratory failure. However, poorly selected ventilator settings can cause further lung damage due to heterogeneity of healthy and damaged alveoli. Varying positive-end-expiratory-pressure (PEEP) to a point of minimum elastance is a lung protective ventilator strategy. However, even low levels of PEEP can lead to ventilator induced lung injury for individuals with highly inflamed pulmonary tissue. Hence, models that could accurately predict peak inspiratory pressures after changes to PEEP could improve clinician confidence in attempting potentially beneficial treatment strategies.

METHODS

This study develops and validates a physiologically relevant respiratory model that captures elastance and resistance via basis functions within a well-validated single compartment lung model. The model can be personalised using information available at a low PEEP to predict lung mechanics at a higher PEEP. Proof of concept validation is undertaken with data from four patients and eight recruitment manoeuvre arms.

RESULTS

Results show low error when predicting upwards over the clinically relevant pressure range, with the model able to predict peak inspiratory pressure with less than 10% error over 90% of the range of PEEP changes up to 12 cmH₂O.

CONCLUSIONS

The results provide an in-silico model-based means of predicting clinically relevant responses to changes in MV therapy, which is the foundation of a first virtual patient for MV.

The risk of invasive cervical cancer among Hispanics: evidence for targeted preventive interventions

BACKGROUND

Mass screening for cervical cancer has considerably reduced invasive cancer rates; however, Hispanic Americans have not fully benefited. This study examined the relationship of demographic, socioeconomic, and acculturation factors to diagnostic stage prior to preventive interventions in a large Hispanic community (San Diego, CA, 1988-1991).

METHODS

Age-adjusted incidence rates (IR) were estimated for three subareas: Hispanic community targeted with interventions, comparison Hispanic community, and remainder of county. Incident cases of cervical cancer in the California Cancer Registry were used to calculate incidence rate ratios (IRR) of in situ to invasive stage cancer and estimate differences in early detection between Hispanics and white non-Hispanics. Multiple logistic regression was used to examine the relationship of cancer stage to census-linked income, education, poverty status, foreign birth, and language spoken.

RESULTS

The in situ cervical cancer IR is significantly lower for Hispanics than for white non-Hispanics in all three regions (P < 0.05). The overall IRR is 3.65 (95% CI 3.19, 4.18) for white non-Hispanics compared with 1.09 (95% CI 0.86, 1.38) for Hispanics. Hispanics in census tracts in the highest versus remaining quartiles for percentage of language-isolated households are at greater risk for invasive stage (OR = 2.10, 95% CI 1.27, 3. 40). White non-Hispanic women residing in census tracts in the highest versus lowest quartile of adults with less than 12 years education are at greater risk for invasive stage (OR = 2.10, 95% CI 1.31, 3.38).

CONCLUSIONS

Results show efforts aimed at cervical cancer early detection for Hispanic women are needed and well targeted. White non-Hispanic women in low-education communities are also at risk. Population-based methods in this study can focus efforts in communities needing preventive interventions.