Effects of human pregnancy and advancing gestation on respiratory discomfort during exercise

Pregnancy reference intervals and exertion and breathlessness ratings for the six minute walk test in healthy nulliparous people

Background

The Six Minute Walk Test (6MWT) is a simple, non-invasive, well-validated test that assesses cardiorespiratory fitness however is rarely used in pregnant people. It may have clinical utilization to assess fitness, breathing and exertion in pregnancy however no reference intervals exist for people 14+0 to 35+6 weeks gestation. We determined the reference intervals for distance walked for the 6MWT, including exertional and breathlessness ratings for this group.

Method

We conducted a prospective observational cohort study of 196 healthy nulliparous pregnant people in earlier pregnancy (EP) 14+0 to 23+6 weeks, and middle pregnancy (MP) 24+0 to 35+6 gestation, who performed a standardized 6MWT protocol including rating exertion and breathlessness (Rating Perceived Exertion (RPE) scale (1 none -15 maximal) and Modified Borg Dyspnea (MBD) scale (0 none - 10 maximal)).

Results

The mean ± SD distance walked was 548 ± 80.9 (EP) versus 547 ± 87.3 (MP) meters (m) P = 0.928. 6MWT reference intervals for the distance walked for the 6MWT were 392-704 m (EP) and 376-718 m (MP). Median (IQR) exertion and breathlessness ratings with exercise for the EP and MP group were 6 (4,7) and 0.5 (0,1) and 6 (4,8) and 0.5 (0,1) respectively. There were no adverse events.

Conclusion

The 6MWT is safe, feasible and acceptable in pregnant people. The reference intervals for the 6MWT are 392-704 m in people 14+0 to 23+6 weeks gestation and 376-718 m for people 24+0 to 35+6 weeks gestation. Exertion was light and breathlessness was just noticeable with the 6MWT.

Assessment of physical fitness during pregnancy: validity and reliability of fitness tests, and relationship with maternal and neonatal health - a systematic review

Objectives

To systematically review studies evaluating one or more components of physical fitness (PF) in pregnant women, to answer two research questions: (1) What tests have been employed to assess PF in pregnant women? and (2) What is the validity and reliability of these tests and their relationship with maternal and neonatal health?

Design

A systematic review.

Data sources

PubMed and Web of Science.

Eligibility criteria

Original English or Spanish full-text articles in a group of healthy pregnant women which at least one component of PF was assessed (field based or laboratory tests).

Results

A total of 149 articles containing a sum of 191 fitness tests were included. Among the 191 fitness tests, 99 (ie, 52%) assessed cardiorespiratory fitness through 75 different protocols, 28 (15%) assessed muscular fitness through 16 different protocols, 14 (7%) assessed flexibility through 13 different protocols, 45 (24%) assessed balance through 40 different protocols, 2 assessed speed with the same protocol and 3 were multidimensional tests using one protocol. A total of 19 articles with 23 tests (13%) assessed either validity (n=4), reliability (n=6) or the relationship of PF with maternal and neonatal health (n=16).

Conclusion

Physical fitness has been assessed through a wide variety of protocols, mostly lacking validity and reliability data, and no consensus exists on the most suitable fitness tests to be performed during pregnancy.

PROSPERO registration number

CRD42018117554.

Prenatal Exercise and Cardiovascular Health (PEACH) Study: impact of pregnancy and exercise on rating of perceived exertion during non-weight-bearing exercise

The purpose of this study was to determine if rating of perceived exertion (RPE) during non-weight-bearing exercise is influenced by gestational age and exercise training. We conducted a randomized controlled trial to examine the influence of gestational age and exercise training (three to four times per week for 25-40 minutes at 50%-70% of heart rate reserve) on RPE during an exhaustive cycling exercise test. We observed no influence of gestational age, or exercise training status on RPE responses to non-weight-bearing exercise during pregnancy. Trial registration number: NCT02948439. Novelty: Gestational age and/or exercise training does not influence rate of perceived exertion during non-weight-bearing exercise.

Impact of ageing and pregnancy on the minute ventilation/carbon dioxide production response to exercise

Ventilatory efficiency can be evaluated using the relationship between minute ventilation (V′_E) and the rate of CO₂ production (V′_CO2). In accordance with the modified alveolar ventilation equation, this relationship is determined by changes in dead space volume (V_D) and/or the arterial CO₂ tension (P_aCO2) equilibrium point. In this review, we summarise the physiological factors that may account for normative ageing and pregnancy induced increases in V′_E/V′_CO2 during exercise. Evidence suggests that age-related increases in V_D and pregnancy-related decreases in the P_aCO2 equilibrium point are mechanistically linked to the increased V′_E/V′_CO2 during exercise. Importantly, the resultant increase in V′_E/V′_CO2 (ratio or slope), with normal ageing or pregnancy, remains below the critical threshold for prognostic indication in cardiopulmonary disease, is not associated with increased risk of adverse health outcomes, and does not affect the respiratory system's ability to fulfil its primary role of eliminating CO₂ and maintaining arterial oxygen saturation during exercise.

The minute ventilation/carbon dioxide production response to exercise is elevated with advancing age and in healthy pregnancy due to increased dead space and lowering of the arterial partial pressure of carbon dioxide equilibrium point, respectively.https://bit.ly/2GJXm0o

Is pelvic floor muscle training able to alter the response of cardiovascular autonomic modulation and provide a possible cardiovascular benefit to pregnant women?

AIMS

To evaluate the acute and chronic effect of an exercise protocol of pelvic floor muscles (PFMs) contraction on the heart period (HP) and systolic arterial pressure (SAP) variabilities and baroreflex sensitivity (BRS) at rest in pregnant women; and to evaluate if this progressive exercise protocol was well-tolerated by the pregnant women studied.

METHODS

We evaluated 48 women at 18 weeks of pregnancy by vaginal palpation, vaginal manometry, and cardiopulmonary exercise test. They were divided in control (CG; 31.75 ± 3.91 years) and training groups (TG; 30.71 ± 3.94 years). At 19 and 36 weeks of pregnancy, electrocardiogram and noninvasive peripheral SAP data were collected at rest before and after 10 PFM contractions. TG performed PFMT from the 20th to the 36th week. HP and SAP variabilities were analyzed by spectral and symbolic analysis. The baroreflex was evaluated by cross-spectral analysis between the HP and SAP series.

RESULTS

The groups did not differ in relation to VO₂ , HP and SAP variabilities, and BRS at the beginning of the protocol. TG increased the endurance of the PFM after training. PFM contraction did not change the HP and SAP variabilities, and BRS at the 18th week. After the training, the TG presented lower SAP mean, lower BF of SAP variability, and higher BRS than CG.

CONCLUSIONS

Acute PFM contractions did not alter HP and SAP variabilities and BRS, but PFMT resulted in a lower SAP mean and higher BRS in trained pregnant when compared to the untrained.

Physical efficiency and activity energy expenditure in term pregnancy females measured during cardiopulmonary exercise tests with a supine cycle ergometer

OBJECTIVES

To evaluate physical efficiency and activity energy expenditure (AEE) in term pregnancy females during cardiopulmonary exercise tests with a supine cycle ergometer.

MATERIAL AND METHODS

The study comprised 22 healthy full-term pregnancy women with uncomplicated pregnancies hospitalized in the Department of Gynecology and Obstetrics, Specialist Teaching Hospital in Tychy, Poland. All subjects underwent cardiopulmonary exercise tests (CPET) on a supine cycle ergometer. The 12-min, three-stage, progressive, symptom-limited submaximal test protocol (up to 80% HRmax) was used. Pulsometry was used to record HR on a beat-to-beat analysis and to calculate AEE. Respiratory responses were measured by ergospirometer and a computer system on a breath-by-breath basis at rest, during exercise and at restitution.

RESULTS

In the studied population, VO2max was established at the level of 2.19 ± 0.33 L/min in ergospirometry and 2.04 ± 025 L/min in pulsometry. Physical efficiency calculated for sub-maximal exercise by use of the Davis equation was 30.52 ± 0.12%. AEE, based on VO2 in various phases of the CPET, was 0.47, 0.71 and 0.88 L/min for phases 25, 50 and 75 W. Based on ergospirometer readouts, AEE was 10.60, 16.11 and 20.94 kJ/min for phases 25, 50 and 75 W. Overall mean AEE (determined by pulsometry) was 10.59  kJ/min. CPET testing did not have any negative effect upon the health or life of the neonates involved in the study.

CONCLUSIONS

Submaximal CPET up to 80% HRmax with a supine cycle ergometer is a safe and precise method for assessing work efficiency in term pregnancy women.

The modified Medical Research Council scale for the assessment of dyspnea in daily living in obesity: a pilot study

Background

Dyspnea is very frequent in obese subjects. However, its assessment is complex in clinical practice. The modified Medical Research Council scale (mMRC scale) is largely used in the assessment of dyspnea in chronic respiratory diseases, but has not been validated in obesity. The objectives of this study were to evaluate the use of the mMRC scale in the assessment of dyspnea in obese subjects and to analyze its relationships with the 6-minute walk test (6MWT), lung function and biological parameters.

Methods

Forty-five obese subjects (17 M/28 F, BMI: 43 ± 9 kg/m²) were included in this pilot study. Dyspnea in daily living was evaluated by the mMRC scale and exertional dyspnea was evaluated by the Borg scale after 6MWT. Pulmonary function tests included spirometry, plethysmography, diffusing capacity of carbon monoxide and arterial blood gases. Fasting blood glucose, total cholesterol, triglyceride, N-terminal pro brain natriuretic peptide, C-reactive protein and hemoglobin levels were analyzed.

Results

Eighty-four percent of patients had a mMRC ≥ 1 and 40% a mMRC ≥ 2. Compared to subjects with no dyspnea (mMRC = 0), a mMRC ≥ 1 was associated with a higher BMI (44 ± 9 vs 36 ± 5 kg/m², p = 0.01), and a lower expiratory reserve volume (ERV) (50 ± 31 vs 91 ± 32%, p = 0.004), forced expiratory volume in one second (FEV₁) (86 ± 17 vs 101 ± 16%, p = 0.04) and distance covered in 6MWT (401 ± 107 vs 524 ± 72 m, p = 0.007). A mMRC ≥ 2 was associated with a higher Borg score after the 6MWT (4.7 ± 2.5 vs 6.5 ± 1.5, p < 0.05).

Conclusion

This study confirms that dyspnea is very frequent in obese subjects. The differences between the “dyspneic” and the “non dyspneic” groups assessed by the mMRC scale for BMI, ERV, FEV₁ and distance covered in 6MWT suggests that the mMRC scale might be an useful and easy-to-use tool to assess dyspnea in daily living in obese subjects.

The impact of human pregnancy on perceptual responses to chemoreflex vs. exercise stimulation of ventilation: a retrospective analysis

We examined the impact of human pregnancy on breathlessness intensity at matched levels of ventilation (V˙E) during isoxic hyperoxic CO₂ rebreathing and incremental cycle exercise tests in 21 healthy women in the third trimester (TM₃) and again ∼5 months post-partum (PP). Pregnancy had no significant (P > 0.05) effect on the slope or threshold of the breathlessness intensity-V˙E relationship during both exercise and rebreathing. By contrast, the slope of the breathlessness intensity-V˙E relationship was significantly higher, while the threshold of this relationship was consistently lower during rebreathing vs. exercise (both P < 0.05), regardless of pregnancy status (P > 0.05). As a result, breathlessness intensity was markedly higher at any given V˙E (e.g., by ∼4 Borg units at 40 L/min) during rebreathing vs. exercise, regardless of pregnancy status. Inter-subject variation in breathlessness intensity-V˙E slopes during exercise was not associated with inter-subject variation in breathlessness intensity-V˙E slopes during rebreathing or with increased central chemoreflex responsiveness during pregnancy (both P > 0.05). In conclusion, the intensity of perceived breathlessness for a given V˙E depends, at least in part, on the nature and source of increased central respiratory motor command output, independent of pregnancy status; and pregnancy-induced increases in activity-related breathlessness cannot be easily explained by increased central chemoreflex responsiveness.

Mechanical ventilatory constraints during incremental cycle exercise in human pregnancy: implications for respiratory sensation

The aim of this study was to identify the physiological mechanisms of exertional respiratory discomfort (breathlessness) in pregnancy by comparing ventilatory (breathing pattern, airway function, operating lung volumes, oesophageal pressure (P(oes))-derived indices of respiratory mechanics) and perceptual (breathlessness intensity) responses to incremental cycle exercise in 15 young, healthy women in the third trimester (TM(3); between 34 and 38 weeks gestation) and again 4-5 months postpartum (PP). During pregnancy, resting inspiratory capacity (IC) increased (P < 0.01) and end-expiratory lung volume decreased (P < 0.001), with no associated change in total lung capacity (TLC) or static respiratory muscle strength. This permitted greater tidal volume (V(T)) expansion throughout exercise in TM(3), while preserving the relationship between contractile respiratory muscle effort (tidal P(oes) swing expressed as a percentage of maximum inspiratory pressure (P(Imax))) and thoracic volume displacement (V(T) expressed as a percentage of vital capacity) and between breathlessness and ventilation . At the highest equivalent work rate (HEWR = 128 +/- 5 W) in TM(3) compared with PP: , tidal P(oes)/P(Imax) and breathlessness intensity ratings increased by 10.2 l min(-1) (P < 0.001), 8.8%P(Imax) (P < 0.05) and 0.9 Borg units (P < 0.05), respectively. Pulmonary resistance was not increased at rest or during exercise at the HEWR in TM(3), despite marked increases in mean tidal inspiratory and expiratory flow rates, suggesting increased bronchodilatation. Dynamic mechanical constraints on V(T) expansion (P < 0.05) with associated increased breathlessness intensity ratings (P < 0.05) were observed near peak exercise in TM(3) compared with PP.

IN CONCLUSION

(1) pregnancy-induced increases in exertional breathlessness reflected the normal awareness of increased and contractile respiratory muscle effort; (2) mechanical adaptations of the respiratory system, including recruitment of resting IC and increased bronchodilatation, accommodated the increased V(T) while preserving effort-displacement and breathlessness-VE relationships; and (3) dynamic mechanical ventilatory constraints contributed to respiratory discomfort near the limits of tolerance in late gestation.

Chemical and mechanical adaptations of the respiratory system at rest and during exercise in human pregnancy

Human pregnancy is characterized by significant increases in ventilatory drive both at rest and during exercise. The increased ventilation and attendant hypocapnia of pregnancy has been attributed primarily to the stimulatory effects of female sex hormones (progesterone and estrogen) on central and peripheral chemoreflex drives to breathe. However, recent research from our laboratory suggests that hormone-mediated increases in neural (or non-chemoreflex) drives to breathe may contribute importantly to the hyperventilation of pregnancy. This review challenges traditional views of ventilatory control, and outlines an alternative hypothesis of the control of breathing during human pregnancy that is currently being tested in our laboratory. Conventional wisdom suggests that pregnancy-induced increases in central respiratory motor output command in combination with progressive thoraco–abdominal distortion may compromise the normal mechanical response of the respiratory system to exercise, increase the perception of exertional breathlessness, and curtail aerobic exercise performance in otherwise healthy pregnant women. The majority of available evidence suggests, however, that neither pregnancy nor advancing gestation are associated with reduced aerobic working capacity or increased breathlessness at any given work rate or ventilation during exhaustive weight-supported exercise.