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Pregnancy Physiology: Cardiovascular, Hematologic and Respiratory System

by Veronica Gillispie, MD, FACOG
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    00:01 So now let's talk about the physiology of pregnancy.

    00:05 So here's a case.

    00:06 Jennie is a 25 year old gravida 1 para 0 female at 34 weeks of gestation.

    00:13 She reports increased difficulty in taking deep breath.

    00:16 She denies shortness of breath on exertion and no chest pain.

    00:19 Her pregnancy has been uncomplicated and she has no medical problems.

    00:24 What is the most likely cause of her difficulty in breathing? And we'll think as we go throughout the lecture.

    00:30 So when we think about the changes of physiology that happen in pregnancy, there are 8 systems that we will want to focus on.

    00:37 First cardiovascular.

    00:39 Next hematologic.

    00:41 Next respiratory.

    00:43 Then the gastrointestinal system.

    00:46 Then the renal system, metabolic, endocrine and anatomical changes that we see throughout the pregnancy.

    00:53 So let's start with the cardiovascular system.

    00:55 First there are some anatomical changes that we need talk about.

    00:58 The heart is displaced left and upward and is rotated on it's long axis in pregnancy.

    01:03 This is important, because when you listen for heart sounds, it's a little different than in a non-pregnant patient.

    01:10 So now let's talk about the physiological changes within the cardiovascular system.

    01:14 So we know that the systemic vascular resistance changes.

    01:17 So how do you think it changes.

    01:19 Does it increase? Does it decrease? Well, in fact it decreases.

    01:24 And this is the reason in the 1st and the 2nd trimester, we notice that the blood pressure also decreases.

    01:30 Well when we think about the main arterial pressure, what do you think happens there? Does it increase? Does it decrease? It in fact decreases as well.

    01:39 Our heart rate also changes in pregnancy.

    01:42 What do you think, does it increase? or does it decrease? The heart rate also increases in pregnancy.

    01:49 And lastly, cardiac output.

    01:50 Do you think it increases or decreases? You probably guessed right.

    01:55 It increases.

    01:56 In fact it increases to almost to 15 to 40% in the 1st trimester and even more during the labor process.

    02:04 So now let's move to the hematologic system.

    02:08 That also changes in pregnancy.

    02:09 First we notice that the blood volume increases to 40 to 45% about the non-pregnant patient.

    02:16 This is mostly because of increase in the erythrocytes and in plasma.

    02:19 And we notice that pregnant woman have physiologic anemia because of this increase.

    02:25 So what else changes.

    02:26 Well our iron requirements also increase in pregnancy.

    02:29 Some of that can be met in the diet but in some pregnant women, they require ion supplementation to meet that increase demand.

    02:36 Now our immune system also changes in pregnancy.

    02:41 We're not exactly sure why that happens.

    02:43 But we do know that the immune system is blunted in pregnancy.

    02:46 Making pregnancy immunodeficient state.

    02:50 Now lastly but most importantly in the hematological system.

    02:53 Pregnant women are hypercoagable.

    02:56 That means their blood is thickened and because of that they are at increased risk for dethrombosis as well as pulmonary embolism.

    03:03 This is important to think about as this can be a huge cause of maternal mortality.

    03:07 Specially in life of patients that undergo C-section.

    03:11 Surgery we know increases our risk of DBT and pregnancy because it is a hypercoagable state.

    03:17 It also increases that risk.

    03:18 So we need to be sure to watch out for that.

    03:22 So now moving on to the respiratory system.

    03:25 There are some anatomic as well as physiologic changes in that system as well.

    03:28 First is the change in the diaphragm.

    03:31 We notice that rises by 4 centimeters.

    03:34 Can you think of why that maybe? Well, let me tell you.

    03:37 The uterus is increasing during that time.

    03:39 As the uterus gets larger, the diaphragm get's pushed up as well.

    03:44 So how does that affect our physiologic changes within the respiratory system.

    03:48 Well the functional residual capacity decreases.

    03:52 And again that's just because the diaphragm is pushing up, so that residual capacity decreases.

    03:57 The total lung volume however does not change.

    04:01 Our expiratory residual volume and our residual volume also decrease.

    04:05 And then when we think of our tidal volume and our minute ventilation, they both increase.

    04:11 So this is a nice diagram that puts all those things that I've just told you, into one big location.

    04:18 So I would make sure that you go through this in a lot of detail to make sure you understand those changes in the lung volume as we've previously discussed.

    04:25 So let's move on to a question.

    04:28 During pregnancy which of the following physiological changes within the pulmonary system? A. Because of compression from the uterus, the total lung capacity (TLC) decreases.

    04:40 B. Because of compression from the uterus, the inspiratory capacity (IC) decreases.

    04:44 C. Because of compression from the uterus, the residual volume (RV) decreases.

    04:49 Or D. None of the above.

    04:50 What do you think? Well, the answer is C.

    04:55 Because of the compression from the uterus, and remember that also causes the diaphragm to decrease by 4 centimeters.

    05:02 The residual volume also decreases.

    05:05 Total lung capacity, inspiratory capacity, those volumes do not change because of pregnancy.


    About the Lecture

    The lecture Pregnancy Physiology: Cardiovascular, Hematologic and Respiratory System by Veronica Gillispie, MD, FACOG is from the course Antenatal Care. It contains the following chapters:

    • Physiology of Pregnancy
    • Cardiovascular System
    • Hematologic System
    • Respiratory System

    Included Quiz Questions

    1. Cardiac output increases due to multiple factors, including an increase in heart rate
    2. Cardiac output increases due to multiple factors, including an increase in mean arterial pressure.
    3. Cardiac output increases due to multiple factors, including a decrease in heart rate and an increase in systemic vascular resistance.
    4. Cardiac output decreases due to multiple factors, including a decrease in blood pressure.
    5. Cardiac output remains the same due to an increase in heart rate and a decrease in mean arterial pressure.
    1. The heart is displaced leftward and upward
    2. The systemic vascular resistance increases
    3. The mean arterial pressure increases
    4. The heart rate decreases
    5. The cardiac output decreases
    1. Maternal blood volume increases by 40-45%.
    2. Maternal iron requirements decrease due to an increase in erythropoiesis .
    3. Maternal immune system is strengthened to protect the fetus from pathogens.
    4. Maternal plasma volume decreases relative to her whole blood volume.
    5. Maternal hypocoagulable state increases risk of abnormal bleeding during pregnancy.
    1. Normal hypercoagulability during pregnancy and immediate post-partum state AND post-operative status.
    2. Post-operative status only
    3. Increased plasma volume during pregnancy
    4. Increased cardiac output during labor and delivery
    5. Physiologic anemia
    1. Decreased end reserve volume
    2. Decreased total lung capacity
    3. Increased total lung capacity
    4. Increased end reserve volume
    5. Decreased tidal volume
    1. The diaphragm rises by 4cm, decreasing functional residual capacity
    2. The diaphragm drops by 4cm, increasing minute ventilation
    3. The diaphragm drops by 4cm, increasing tidal volume
    4. The diaphragm rises by 4cm, increasing residual volume
    5. The diaphragm rises by 4cm, decreasing total lung capacity

    Author of lecture Pregnancy Physiology: Cardiovascular, Hematologic and Respiratory System

     Veronica Gillispie, MD, FACOG

    Veronica Gillispie, MD, FACOG


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