We have entered into various foreign currency debt obligations. As of March 31, 2019, the total principal amount of foreign currency debt obligations was $4.4 billion, including $3.1 billion denominated in Euro, $617.3 million denominated in British Pound, $417.7 million denominated in Japanese Yen and $286.3 million denominated in Swedish Krona. As of March 31, 2019, we have designated $4.1 billion of the total principal amount of foreign currency debt obligations as net investment hedges against our net investments in foreign subsidiaries. For a net investment hedge, changes in the fair value of the hedging instrument designated as a net investment hedge, except forward points, are recorded as a component of other comprehensive income (loss) in the consolidated balance sheets. Fluctuations in the exchange rates between these foreign currencies (i.e. Euro, British Pound, Swedish Krona and Japanese Yen) and the U.S. Dollar will impact the amount of U.S. Dollars that we will require to settle the foreign currency debt obligations at maturity. If the U.S. Dollar would have been weaker or stronger by 10% in comparison to these foreign currencies as of March 31, 2019, we estimate our obligation to cash settle the principal of these foreign currency debt obligations in U.S. Dollars would have increased or decreased by approximately $489.7 million and $400.6 million, respectively.
In 2019, we also entered into cross-currency interest rate swaps where we receive a fixed amount of U.S. Dollars and pay a fixed amount of Euros, with a total notional amount of $750.0 million. The cross-currency interest rate swaps are designated as hedges of our net investment in its European operations and changes in the fair value of these swaps are recorded as a component of accumulated other comprehensive income (loss) in the condensed consolidated balance sheet. If the U.S. Dollar weakened or strengthened by 10% in comparison to Euro, the amount recorded in accumulated other comprehensive income (loss) related to the cross-currency interest rate swaps would have been approximately $94.6 million lower or $77.4 million higher as of March 31, 2019.
The U.S. Dollar strengthened relative to certain of the currencies of the foreign countries in which we operate during the three months ended March 31, 2019. This has impacted our condensed consolidated financial position and results of operations during this period, including the amount of revenues that we reported. Continued strengthening or weakening of the U.S. Dollar will continue to impact us in future periods.
With the existing cash flow hedges in place, a hypothetical additional 10% strengthening of the U.S. Dollar for the three months ended March 31, 2019 would have resulted in a reduction of our revenues and operating expenses including depreciation and amortization expense by approximately $39.4 million and $37.5 million, respectively.
With the existing cash flow hedges in place, a hypothetical additional 10% weakening of the U.S. Dollar for the three months ended March 31, 2019 would have resulted in an increase of our revenues and operating expenses including depreciation and amortization expense by approximately $47.2 million and $46.1 million, respectively.
Interest Rate Risk
We are exposed to interest rate risk related to our outstanding debt. An immediate 10% increase or decrease in current interest rates from their position as of March 31, 2019 would not have a material impact on our interest expense due to the fixed coupon rate on the majority of our debt obligations. However, the interest expense associated with our senior credit facility and term loans, that bear interest at variable rates, could be affected. For every 100 basis point increase or decrease in interest rates, our annual interest expense could increase by a total of approximately $12.9 million or decrease by a total of approximately $5.3 million based on the total balance of our primary borrowings under the Term Loan Facility as of March 31, 2019. As of March 31, 2019, we had not employed any interest rate derivative products against our debt obligations. However, we may enter into interest rate hedging agreements in the future to mitigate our exposure to interest rate risk.
Controls and Procedures
(a) Evaluation of Disclosure Controls and Procedures. Our management, with the participation of our Chief Executive Officer and our Chief Financial Officer, conducted an evaluation, pursuant to Rule 13a-15 promulgated under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), of the effectiveness of our "disclosure controls and procedures" as of the end of the period covered by this quarterly report. Based on this evaluation, the Chief Executive Officer and Chief Financial Officer concluded that the disclosure controls and procedures were effective as of the end of the period covered by this quarterly report.
(b) Changes in Internal Control over Financial Reporting. There were no changes in our internal control over financial reporting identified in connection with the evaluation required by Rules 13a-15(d) and 15d-15(d) of the Exchange Act that occurred during the three months ended March 31, 2019 that have materially affected, or are reasonably likely to materially affect, our internal control over financial reporting. While we implemented certain internal controls related to the adoption of ASC 842, Leases, to ensure we adequately evaluated our contracts and properly assessed the impact of the new lease accounting standard