Maternal Physiology: Body Water Metabolism
CHAPTER 3
Maternal Physiology
Michael C. Gordon
Body Water Metabolism
42
Osmoregulation 43
Salt Metabolism 43
Renin-Angiotensin-Aldosterone System 43
Atrial and Brain Natriuretic Peptide 44
Cardiovascular System
44
Heart 44
Cardiac Output 45
Arterial Blood Pressure and Systemic
Vascular Resistance 46
Venous Pressure 47
Central Hemodynamic Assessment 47
Normal Changes That Mimic Heart
Disease 47
Effect of Labor and the Immediate
Puerperium 48
Respiratory System
49
Upper Respiratory Tract 49
Mechanical Changes 49
Lung Volume and Pulmonary Function 49
Gas Exchange 50
Sleep 51
Hematologic Changes
Urinary System
42
54
Anatomic Changes 54
Renal Hemodynamics 54
Renal Tubular Function/Excretion of Nutrients …show more content…
However, in certain cardiac diseases, maternal morbidity and even mortality may occur.
Heart
The combination of displacement of the diaphragm and the effect of pregnancy on the shape of the rib cage
(described in the respiratory section below) displaces the heart upward and to the left. In addition, the heart rotates on its long axis, moving the apex somewhat laterally, resulting in an increased cardiac silhouette on radiographic studies, without a true change in the cardiothoracic ratio.
Associated radiographic findings include an apparent straightening of the border of the left side of the heart and increased prominence of the pulmonary conus. Therefore, the diagnosis of cardiomegaly by simple radiography should be confirmed by echocardiogram if clinically appropriate.10
Although true cardiomegaly is rare, physiologic myocardial hypertrophy of the heart is consistently observed as a result of expanded blood volume in the first half of the pregnancy and progressively increasing afterload in later gestation. These structural changes in the heart are similar to those found in response to exercise and result in …show more content…
In a longitudinal study by Robson and associates using Doppler echocardiography, CO increased by 50% at 34 weeks from a prepregnancy value of
4.88 L/min to 7.34 L/min19,20 (Figure 3-2). In twin gestations, CO incrementally increases an additional 20% above that of singleton pregnancies.13 Robson and associates demonstrated that, by 5 weeks’ gestation, CO has already risen by more than 10%. By 12 weeks, the rise in output is 34% to
39% above nongravid levels, accounting for about 75% of the total increase in CO during pregnancy. Although the literature is not clear regarding the exact gestation when
CO peaks, most studies point to a range between 25 and
30 weeks.20 The data on whether the CO continues to increase in the third trimester are very divergent, with equal numbers of good longitudinal studies showing a mild decrease, a slight increase, or no change.19 The differences in these studies cannot be explained by differences in investigative techniques, position of the women during measurements, or study design. This apparent discrepancy
Maternal Physiology
Michael C. Gordon
Body Water Metabolism
42
Osmoregulation 43
Salt Metabolism 43
Renin-Angiotensin-Aldosterone System 43
Atrial and Brain Natriuretic Peptide 44
Cardiovascular System
44
Heart 44
Cardiac Output 45
Arterial Blood Pressure and Systemic
Vascular Resistance 46
Venous Pressure 47
Central Hemodynamic Assessment 47
Normal Changes That Mimic Heart
Disease 47
Effect of Labor and the Immediate
Puerperium 48
Respiratory System
49
Upper Respiratory Tract 49
Mechanical Changes 49
Lung Volume and Pulmonary Function 49
Gas Exchange 50
Sleep 51
Hematologic Changes
Urinary System
42
54
Anatomic Changes 54
Renal Hemodynamics 54
Renal Tubular Function/Excretion of Nutrients …show more content…
However, in certain cardiac diseases, maternal morbidity and even mortality may occur.
Heart
The combination of displacement of the diaphragm and the effect of pregnancy on the shape of the rib cage
(described in the respiratory section below) displaces the heart upward and to the left. In addition, the heart rotates on its long axis, moving the apex somewhat laterally, resulting in an increased cardiac silhouette on radiographic studies, without a true change in the cardiothoracic ratio.
Associated radiographic findings include an apparent straightening of the border of the left side of the heart and increased prominence of the pulmonary conus. Therefore, the diagnosis of cardiomegaly by simple radiography should be confirmed by echocardiogram if clinically appropriate.10
Although true cardiomegaly is rare, physiologic myocardial hypertrophy of the heart is consistently observed as a result of expanded blood volume in the first half of the pregnancy and progressively increasing afterload in later gestation. These structural changes in the heart are similar to those found in response to exercise and result in …show more content…
In a longitudinal study by Robson and associates using Doppler echocardiography, CO increased by 50% at 34 weeks from a prepregnancy value of
4.88 L/min to 7.34 L/min19,20 (Figure 3-2). In twin gestations, CO incrementally increases an additional 20% above that of singleton pregnancies.13 Robson and associates demonstrated that, by 5 weeks’ gestation, CO has already risen by more than 10%. By 12 weeks, the rise in output is 34% to
39% above nongravid levels, accounting for about 75% of the total increase in CO during pregnancy. Although the literature is not clear regarding the exact gestation when
CO peaks, most studies point to a range between 25 and
30 weeks.20 The data on whether the CO continues to increase in the third trimester are very divergent, with equal numbers of good longitudinal studies showing a mild decrease, a slight increase, or no change.19 The differences in these studies cannot be explained by differences in investigative techniques, position of the women during measurements, or study design. This apparent discrepancy